Fixed an error message

OS/01/device.py

@@ -201,7 +201,7 @@ if __name__ == "__main__":
         # Configuration for WebSocket
         WS_URL = os.getenv('SERVER_CONNECTION_URL')
         if not WS_URL:
-            raise ValueError("The environment variable SERVER_URL is not set. Please set it to proceed.")
+            raise ValueError("The environment variable SERVER_CONNECTION_URL is not set. Please set it to proceed.")
 
         # Start the WebSocket communication
         asyncio.create_task(websocket_communication(WS_URL))