Getting "NSURLErrorDomain error 1" while connecting WebSocket

I am trying to connect WebSocket using URLSessionWebSocketTask for a Safari Web Extension,

And I have added receive function for getting messages, like this

        webSocketTask.receive { result in
            switch result {
            case .failure(let error):
                print("Failed to receive message: \(error.localizedDescription)")
            case .success(let message):
            .
            .
            and the rest of the code...

And I am getting error.localizedDescription like this:

"The operation couldn’t be completed. (NSURLErrorDomain error 1.)".

My URL for socket connection is like this (myconnection is placeholder here for actual value, as I can't share it here):

wss://127.0.0.1:10001" + "/myconnection" 

This looks like a very generic message on failure.

Can anyone help me find out what this "error 1" code means?