Fix crash where user_id are not strings

sync/ws_sender.py

@@ -48,6 +48,8 @@ class WebSocketSender:
         - user_ids: A single user_id or a list/set of user_ids.
         - device_id: The message content/identifier to send.
         """
+
+        user_ids = [str(user_id) for user_id in user_ids]
         if not isinstance(user_ids, (list, set, tuple)):
             user_ids = [user_ids]