diff --git a/src/api_request_handler.rs b/src/api_request_handler.rs
index 257fa1a..c0660ec 100644
--- a/src/api_request_handler.rs
+++ b/src/api_request_handler.rs
@@ -59,9 +59,9 @@ impl APIHandler {
             return Ok(Response::builder()
                 .header("Content-Type", "text/html")
                 .header("Access-Control-Allow-Origin", "*")
-                .body(Full::new(Bytes::from_static(
-                    include_bytes!("./index.html"),
-                )))?);
+                .body(Full::new(Bytes::from_static(include_bytes!(
+                    "./index.html"
+                ))))?);
         }
 
         // If not, handle the request as a normal API request.
@@ -120,11 +120,8 @@ impl APIHandler {
 
         let new_notification_manager = self.notification_manager.clone();
         tokio::spawn(async move {
-            match RelayConnection::run(websocket, new_notification_manager).await {
-                Ok(_) => {}
-                Err(e) => {
-                    log::error!("Error with websocket connection: {:?}", e);
-                }
+            if let Err(e) = RelayConnection::run(websocket, new_notification_manager).await {
+                log::error!("Error with websocket connection: {}", e.to_string());
             }
         });
 
@@ -135,7 +132,7 @@ impl APIHandler {
         &self,
         mut req: Request<Incoming>,
         config: &NotePushConfig,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let parsed_request = self.parse_http_request(&mut req).await?;
         let api_response: APIResponse = self
             .handle_parsed_http_request(&parsed_request, config)
@@ -147,7 +144,7 @@ impl APIHandler {
     async fn parse_http_request(
         &self,
         req: &mut Request<Incoming>,
-    ) -> Result<ParsedRequest, Box<dyn std::error::Error>> {
+    ) -> Result<ParsedRequest, Box<dyn std::error::Error + Send + Sync>> {
         // 1. Read the request body
         let body_buffer = req.body_mut().collect().await?.aggregate();
         let body_bytes = body_buffer.chunk();
@@ -187,7 +184,7 @@ impl APIHandler {
         &self,
         parsed_request: &ParsedRequest,
         config: &NotePushConfig,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         enum RouteMatch {
             UserInfo,
             UserSetting,
@@ -261,7 +258,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let device_token = get_required_param(&url_params, "deviceToken")?;
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
@@ -293,7 +290,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let device_token = get_required_param(&url_params, "deviceToken")?;
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
@@ -310,7 +307,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
 
@@ -323,7 +320,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
         let target = get_required_param(&url_params, "target")?;
@@ -350,7 +347,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
         let target = get_required_param(&url_params, "target")?;
@@ -367,7 +364,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let device_token = get_required_param(&url_params, "deviceToken")?;
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
@@ -393,7 +390,7 @@ impl APIHandler {
         &self,
         req: &ParsedRequest,
         url_params: Params<'_, '_>,
-    ) -> Result<APIResponse, Box<dyn std::error::Error>> {
+    ) -> Result<APIResponse, Box<dyn std::error::Error + Send + Sync>> {
         let device_token = get_required_param(&url_params, "deviceToken")?;
         let pubkey = get_required_param(&url_params, "pubkey")?;
         let pubkey = check_pubkey(&pubkey, req)?;
@@ -401,7 +398,7 @@ impl APIHandler {
         // Proceed with the main logic after passing all checks
         let settings = self
             .notification_manager
-            .get_user_notification_settings(&pubkey, device_token.to_string())
+            .get_user_notification_settings(&pubkey, &device_token)
             .await?;
 
         Ok(APIResponse::ok_body(&settings))
diff --git a/src/notification_manager/mod.rs b/src/notification_manager/mod.rs
index 9393c6b..afa8012 100644
--- a/src/notification_manager/mod.rs
+++ b/src/notification_manager/mod.rs
@@ -82,8 +82,13 @@ pub enum NotificationManagerError {
     APNSMissing,
     #[error("FCM is not configured")]
     FCMMissing,
+
+    #[error(transparent)]
+    Other(BoxSendError),
 }
 
+type BoxSendError = Box<dyn std::error::Error + Send + Sync>;
+type NResult<T> = Result<T, BoxSendError>;
 type DatabaseArc = Arc<Mutex<r2d2::Pool<SqliteConnectionManager>>>;
 
 pub struct NotificationManager {
@@ -105,10 +110,7 @@ impl EventSaver {
         Self { db }
     }
 
-    pub async fn save_if_needed(
-        &self,
-        event: &nostr::Event,
-    ) -> Result<bool, Box<dyn std::error::Error>> {
+    pub async fn save_if_needed(&self, event: &nostr::Event) -> NResult<bool> {
         match event.to_mute_list() {
             Some(mute_list) => {
                 match self
@@ -144,7 +146,7 @@ impl EventSaver {
         pubkey: PublicKey,
         mute_list: MuteList,
         created_at: Timestamp,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         let mute_list_json = mute_list.to_json()?;
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
@@ -167,7 +169,7 @@ impl EventSaver {
     pub async fn get_saved_mute_list_for(
         &self,
         pubkey: PublicKey,
-    ) -> Result<Option<TimestampedMuteList>, Box<dyn std::error::Error>> {
+    ) -> NResult<Option<TimestampedMuteList>> {
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
 
@@ -175,11 +177,11 @@ impl EventSaver {
             "SELECT mute_list, created_at FROM muting_preferences WHERE user_pubkey = ?",
         )?;
 
-        let mute_list_info: (serde_json::Value, nostr::Timestamp) = match stmt
+        let mute_list_info: (serde_json::Value, Timestamp) = match stmt
             .query_row([pubkey.to_sql_string()], |row| {
                 Ok((row.get(0)?, row.get(1)?))
             }) {
-            Ok(info) => (info.0, nostr::Timestamp::from_sql_string(info.1)?),
+            Ok(info) => (info.0, Timestamp::from_sql_string(info.1)?),
             Err(rusqlite::Error::QueryReturnedNoRows) => return Ok(None),
             Err(e) => return Err(e.into()),
         };
@@ -202,7 +204,7 @@ impl NotificationManager {
         db: r2d2::Pool<SqliteConnectionManager>,
         relay_url: String,
         cache_max_age: std::time::Duration,
-    ) -> Result<Self, Box<dyn std::error::Error>> {
+    ) -> NResult<Self> {
         let connection = db.get()?;
         Self::setup_database(&connection)?;
 
@@ -234,7 +236,7 @@ impl NotificationManager {
         apns_team_id: String,
         apns_environment: a2::client::Endpoint,
         apns_topic: String,
-    ) -> Result<Self, Box<dyn std::error::Error>> {
+    ) -> NResult<Self> {
         let mut file = File::open(&apns_private_key_path)?;
 
         let client = Client::token(
@@ -250,16 +252,13 @@ impl NotificationManager {
         Ok(self)
     }
 
-    pub fn with_fcm(
-        mut self,
-        google_services_file_path: impl Into<String>
-    ) -> Result<Self, Box<dyn std::error::Error>> {
+    pub fn with_fcm(mut self, google_services_file_path: impl Into<String>) -> NResult<Self> {
         self.fcm_client
             .replace(Mutex::new(FcmService::new(google_services_file_path)));
         Ok(self)
     }
 
-    pub async fn handle_event(&self, event: &Event) -> Result<(), Box<dyn std::error::Error>> {
+    pub async fn handle_event(&self, event: &Event) -> NResult<()> {
         log::info!(
             "Received event kind={},id={}",
             event.kind.as_u32(),
@@ -427,10 +426,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
 
     // MARK: - "Business" logic
 
-    pub async fn send_notifications_if_needed(
-        &self,
-        event: &Event,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    pub async fn send_notifications_if_needed(&self, event: &Event) -> NResult<()> {
         log::debug!(
             "Checking if notifications need to be sent for event: {}",
             event.id
@@ -469,21 +465,29 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         );
 
         for pubkey in pubkeys_to_notify {
-            self.send_event_notifications_to_pubkey(event, &pubkey)
-                .await?;
+            match self
+                .send_event_notifications_to_pubkey(event, &pubkey)
+                .await
             {
-                let db_mutex_guard = self.db.lock().await;
-                db_mutex_guard.get()?.execute(
-                    "INSERT OR REPLACE INTO notifications (id, event_id, pubkey, received_notification, sent_at)
+                Ok(_) => {
+                    let db_mutex_guard = self.db.lock().await;
+                    db_mutex_guard.get()?.execute(
+                        "INSERT OR REPLACE INTO notifications (id, event_id, pubkey, received_notification, sent_at)
                     VALUES (?, ?, ?, ?, ?)",
-                    params![
-                        format!("{}:{}", event.id, pubkey),
-                        event.notification_id(),
-                        pubkey.to_sql_string(),
-                        true,
-                        Timestamp::now().to_sql_string(),
-                    ],
-                )?;
+                        params![
+                            format!("{}:{}", event.id, pubkey),
+                            event.notification_id(),
+                            pubkey.to_sql_string(),
+                            true,
+                            Timestamp::now().to_sql_string(),
+                        ],
+                    )?;
+                }
+                Err(e) => log::warn!(
+                    "Error while sending notifications to {}: {}",
+                    pubkey.to_hex(),
+                    e.to_string()
+                ),
             }
         }
         Ok(())
@@ -507,10 +511,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         Self::supported_kinds().contains(&event_kind)
     }
 
-    async fn pubkeys_to_notify_for_event(
-        &self,
-        event: &Event,
-    ) -> Result<HashSet<PublicKey>, Box<dyn std::error::Error>> {
+    async fn pubkeys_to_notify_for_event(&self, event: &Event) -> NResult<HashSet<PublicKey>> {
         let notification_status = self.get_notification_status(event).await?;
         let relevant_pubkeys = self.pubkeys_relevant_to_event(event).await?;
         let mut relevant_pubkeys_that_are_registered = HashSet::new();
@@ -557,7 +558,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
     async fn get_newest_mute_list_available(
         &self,
         pubkey: &PublicKey,
-    ) -> Result<Option<MuteList>, Box<dyn std::error::Error>> {
+    ) -> NResult<Option<MuteList>> {
         let timestamped_saved_mute_list = self.event_saver.get_saved_mute_list_for(*pubkey).await?;
         let timestamped_network_mute_list =
             self.nostr_network_helper.get_public_mute_list(pubkey).await;
@@ -588,10 +589,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         )
     }
 
-    async fn pubkeys_relevant_to_event(
-        &self,
-        event: &Event,
-    ) -> Result<HashSet<PublicKey>, Box<dyn std::error::Error>> {
+    async fn pubkeys_relevant_to_event(&self, event: &Event) -> NResult<HashSet<PublicKey>> {
         let mut direct_keys = event.relevant_pubkeys();
         let fake_target = match event.kind {
             // accept p tagged host as target for notifications in live event
@@ -639,17 +637,22 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         &self,
         event: &Event,
         pubkey: &PublicKey,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         let user_device_tokens = self.get_user_device_tokens(pubkey).await?;
         for (device_token, backend) in user_device_tokens {
-            if !self
-                .user_wants_notification(pubkey, device_token.clone(), event)
-                .await?
-            {
+            let wants_notif = self
+                .user_wants_notification(pubkey, &device_token, event)
+                .await?;
+            if !wants_notif {
                 continue;
             }
-            self.send_event_notification_to_device_token(event, &device_token, backend)
-                .await?;
+            // as long as we send to at least one device for each user we consider it a success
+            if let Err(e) = self
+                .send_event_notification_to_device_token(event, &device_token, backend)
+                .await
+            {
+                log::warn!("Failed to send notification to {}: {}", &device_token, e);
+            }
         }
         Ok(())
     }
@@ -657,9 +660,9 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
     async fn user_wants_notification(
         &self,
         pubkey: &PublicKey,
-        device_token: String,
+        device_token: &str,
         event: &Event,
-    ) -> Result<bool, Box<dyn std::error::Error>> {
+    ) -> NResult<bool> {
         let notification_preferences = self
             .get_user_notification_settings(pubkey, device_token)
             .await?;
@@ -683,31 +686,14 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         Ok(notification_preferences.merge_kinds().contains(&event.kind))
     }
 
-    async fn is_pubkey_token_pair_registered(
-        &self,
-        pubkey: &PublicKey,
-        device_token: &str,
-    ) -> Result<bool, Box<dyn std::error::Error>> {
-        let current_device_tokens: Vec<String> = self
-            .get_user_device_tokens(pubkey)
-            .await?
-            .into_iter()
-            .map(|(d, _)| d)
-            .collect();
-        Ok(current_device_tokens.contains(&device_token.to_string()))
-    }
-
-    async fn is_pubkey_registered(
-        &self,
-        pubkey: &PublicKey,
-    ) -> Result<bool, Box<dyn std::error::Error>> {
+    async fn is_pubkey_registered(&self, pubkey: &PublicKey) -> NResult<bool> {
         Ok(!self.get_user_device_tokens(pubkey).await?.is_empty())
     }
 
     async fn get_notify_from_target(
         &self,
         target: &PublicKey,
-    ) -> Result<Vec<(PublicKey, Vec<Kind>)>, Box<dyn std::error::Error>> {
+    ) -> NResult<Vec<(PublicKey, Vec<Kind>)>> {
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
         let mut stmt =
@@ -732,7 +718,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
     async fn get_user_device_tokens(
         &self,
         pubkey: &PublicKey,
-    ) -> Result<Vec<(String, NotificationBackend)>, Box<dyn std::error::Error>> {
+    ) -> NResult<Vec<(String, NotificationBackend)>> {
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
         let mut stmt =
@@ -749,10 +735,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         Ok(device_tokens)
     }
 
-    async fn get_notification_status(
-        &self,
-        event: &Event,
-    ) -> Result<NotificationStatus, Box<dyn std::error::Error>> {
+    async fn get_notification_status(&self, event: &Event) -> NResult<NotificationStatus> {
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
         let mut stmt = connection.prepare(
@@ -785,7 +768,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         event: &Event,
         device_token: &str,
         backend: NotificationBackend,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         log::debug!("Sending notification to device token: {}", device_token);
 
         match &backend {
@@ -803,11 +786,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         Ok(())
     }
 
-    async fn send_event_notification_apns(
-        &self,
-        event: &Event,
-        device_token: &str,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    async fn send_event_notification_apns(&self, event: &Event, device_token: &str) -> NResult<()> {
         let client = self
             .apns_client
             .as_ref()
@@ -842,11 +821,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         Ok(())
     }
 
-    async fn send_event_notification_fcm(
-        &self,
-        event: &Event,
-        device_token: &str,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    async fn send_event_notification_fcm(&self, event: &Event, device_token: &str) -> NResult<()> {
         let client = self
             .fcm_client
             .as_ref()
@@ -865,7 +840,10 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
             "nostr_event".to_string(),
             event.as_json(),
         )])));
-        client.send_notification(msg).await?;
+        client
+            .send_notification(msg)
+            .await
+            .map_err(|e| e.to_string())?;
 
         Ok(())
     }
@@ -915,7 +893,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         pubkey: PublicKey,
         device_token: &str,
         backend: NotificationBackend,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         let current_time_unix = Timestamp::now();
         let db_mutex_guard = self.db.lock().await;
         db_mutex_guard.get()?.execute(
@@ -935,7 +913,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         &self,
         pubkey: &PublicKey,
         device_token: &str,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         let db_mutex_guard = self.db.lock().await;
         db_mutex_guard.get()?.execute(
             "DELETE FROM user_info WHERE pubkey = ? AND device_token = ?",
@@ -944,10 +922,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         Ok(())
     }
 
-    pub async fn get_notify_keys(
-        &self,
-        pubkey: PublicKey,
-    ) -> Result<Vec<PublicKey>, Box<dyn std::error::Error>> {
+    pub async fn get_notify_keys(&self, pubkey: PublicKey) -> NResult<Vec<PublicKey>> {
         let db_mutex_guard = self.db.lock().await;
         let conn = db_mutex_guard.get()?;
         let mut stmt =
@@ -967,7 +942,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         pubkey: PublicKey,
         target: PublicKey,
         kinds: Vec<Kind>,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         let current_time_unix = Timestamp::now();
         let db_mutex_guard = self.db.lock().await;
         db_mutex_guard.get()?.execute(
@@ -977,16 +952,12 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
                 target.to_sql_string(),
                 current_time_unix.to_sql_string(),
                 kinds.iter().map(|k| k.as_u32().to_string()).collect::<Vec<String>>().join(",")
-            ]
+            ],
         )?;
         Ok(())
     }
 
-    pub async fn delete_notify_key(
-        &self,
-        pubkey: PublicKey,
-        target: PublicKey,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    pub async fn delete_notify_key(&self, pubkey: PublicKey, target: PublicKey) -> NResult<()> {
         let db_mutex_guard = self.db.lock().await;
         db_mutex_guard.get()?.execute(
             "delete from notify_keys where user_pubkey = ? and target_pubkey = ?",
@@ -998,14 +969,14 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
     pub async fn get_user_notification_settings(
         &self,
         pubkey: &PublicKey,
-        device_token: String,
-    ) -> Result<UserNotificationSettings, Box<dyn std::error::Error>> {
+        device_token: &str,
+    ) -> NResult<UserNotificationSettings> {
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
         let mut stmt = connection.prepare(
             "SELECT kinds, only_notifications_from_following_enabled, hellthread_notifications_disabled, hellthread_notifications_max_pubkeys FROM user_info WHERE pubkey = ? AND device_token = ?",
         )?;
-        let settings = stmt.query_row([pubkey.to_sql_string(), device_token], |row| {
+        let settings = stmt.query_row([pubkey.to_sql_string().as_str(), device_token], |row| {
             let kinds: String = row.get(0)?;
             let kinds: Vec<Kind> = kinds
                 .split(',')
@@ -1036,7 +1007,7 @@ ALTER TABLE user_info drop column dm_notifications_enabled;",
         pubkey: &PublicKey,
         device_token: String,
         settings: UserNotificationSettings,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> NResult<()> {
         let db_mutex_guard = self.db.lock().await;
         let connection = db_mutex_guard.get()?;
         connection.execute(
diff --git a/src/notification_manager/nostr_event_extensions.rs b/src/notification_manager/nostr_event_extensions.rs
index fa3d18c..77cc90c 100644
--- a/src/notification_manager/nostr_event_extensions.rs
+++ b/src/notification_manager/nostr_event_extensions.rs
@@ -80,7 +80,7 @@ impl ExtendedEvent for nostr::Event {
 
 pub trait SqlStringConvertible {
     fn to_sql_string(&self) -> String;
-    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error>>
+    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error + Send + Sync>>
     where
         Self: Sized;
 }
@@ -90,7 +90,7 @@ impl SqlStringConvertible for nostr::EventId {
         self.to_hex()
     }
 
-    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error>> {
+    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error + Send + Sync>> {
         nostr::EventId::from_hex(s).map_err(|e| e.into())
     }
 }
@@ -100,7 +100,7 @@ impl SqlStringConvertible for nostr::PublicKey {
         self.to_hex()
     }
 
-    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error>> {
+    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error + Send + Sync>> {
         PublicKey::from_hex(s).map_err(|e| e.into())
     }
 }
@@ -110,7 +110,7 @@ impl SqlStringConvertible for nostr::Timestamp {
         self.as_u64().to_string()
     }
 
-    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error>> {
+    fn from_sql_string(s: String) -> Result<Self, Box<dyn std::error::Error + Send + Sync>> {
         let u64_timestamp: u64 = s.parse()?;
         Ok(nostr::Timestamp::from(u64_timestamp))
     }
@@ -180,14 +180,14 @@ impl MaybeConvertibleToRelayList for nostr::Event {
 /// A trait for types that can be encoded to and decoded from JSON, specific to this crate.
 /// This is defined to overcome the rust compiler's limitation of implementing a trait for a type that is not defined in the same crate.
 pub trait Codable {
-    fn to_json(&self) -> Result<serde_json::Value, Box<dyn std::error::Error>>;
-    fn from_json(json: serde_json::Value) -> Result<Self, Box<dyn std::error::Error>>
+    fn to_json(&self) -> Result<serde_json::Value, Box<dyn std::error::Error + Send + Sync>>;
+    fn from_json(json: serde_json::Value) -> Result<Self, Box<dyn std::error::Error + Send + Sync>>
     where
         Self: Sized;
 }
 
 impl Codable for MuteList {
-    fn to_json(&self) -> Result<serde_json::Value, Box<dyn std::error::Error>> {
+    fn to_json(&self) -> Result<serde_json::Value, Box<dyn std::error::Error + Send + Sync>> {
         Ok(serde_json::json!({
             "public_keys": self.public_keys.iter().map(|pk| pk.to_hex()).collect::<Vec<String>>(),
             "hashtags": self.hashtags.clone(),
@@ -196,7 +196,7 @@ impl Codable for MuteList {
         }))
     }
 
-    fn from_json(json: serde_json::Value) -> Result<Self, Box<dyn std::error::Error>>
+    fn from_json(json: serde_json::Value) -> Result<Self, Box<dyn std::error::Error + Send + Sync>>
     where
         Self: Sized,
     {
diff --git a/src/notification_manager/nostr_network_helper.rs b/src/notification_manager/nostr_network_helper.rs
index da84cbc..4262b53 100644
--- a/src/notification_manager/nostr_network_helper.rs
+++ b/src/notification_manager/nostr_network_helper.rs
@@ -21,7 +21,7 @@ impl NostrNetworkHelper {
         relay_url: String,
         cache_max_age: Duration,
         event_saver: EventSaver,
-    ) -> Result<Self, Box<dyn std::error::Error>> {
+    ) -> Result<Self, Box<dyn std::error::Error + Send + Sync>> {
         let client = Client::new(Keys::generate());
         client.add_relay(relay_url.clone()).await?;
         client.connect().await;
diff --git a/src/relay_connection.rs b/src/relay_connection.rs
index 354a5a5..d16f517 100644
--- a/src/relay_connection.rs
+++ b/src/relay_connection.rs
@@ -72,7 +72,7 @@ impl RelayConnection {
         &mut self,
         raw_message: Result<Message, Error>,
         stream: &mut WebSocketStream<TokioIo<Upgraded>>,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
         let raw_message = raw_message?;
         self.run_loop_iteration(raw_message, stream).await
     }
@@ -81,7 +81,7 @@ impl RelayConnection {
         &mut self,
         raw_message: Message,
         stream: &mut WebSocketStream<TokioIo<Upgraded>>,
-    ) -> Result<(), Box<dyn std::error::Error>> {
+    ) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
         if raw_message.is_text() {
             let message: ClientMessage =
                 ClientMessage::from_value(Value::from_str(raw_message.to_text()?)?)?;
@@ -98,7 +98,7 @@ impl RelayConnection {
     async fn handle_client_message(
         &self,
         message: ClientMessage,
-    ) -> Result<RelayMessage, Box<dyn std::error::Error>> {
+    ) -> Result<RelayMessage, Box<dyn std::error::Error + Send + Sync>> {
         match message {
             ClientMessage::Event(event) => {
                 self.notification_manager.handle_event(&event).await?;