bad response from the server

Got this error when trying to setup Websocket
server.traccar.org (subscription)

WebSocket error: Error Domain=NSURLErrorDomain Code=-1011 "There was a bad response from the server." UserInfo={NSErrorFailingURLStringKey=https://server.traccar.org/api/socket, NSErrorFailingURLKey=https://server.traccar.org/api/socket, _NSURLErrorWebSocketHandshakeFailureReasonKey=0, NSLocalizedDescription=There was a bad response from the server.}
WebSocket send error: Error Domain=NSURLErrorDomain Code=-1011 "There was a bad response from the server." UserInfo={NSErrorFailingURLStringKey=https://server.traccar.org/api/socket, NSErrorFailingURLKey=https://server.traccar.org/api/socket, _NSURLErrorWebSocketHandshakeFailureReasonKey=0, NSLocalizedDescription=There was a bad response from the server.}

session is 200. cookie received.
Please how to fix it?

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