How have continuing conversation with XMLHttpRequest?

I’ve gotten it so my XMLHttpRequest is able to send a synchronous call to a non-http url and get a response. But after getting the response, how do I send another message to the remote server?

Whenever I try to call xmlHttpRequest.send(…) again, it tells me the state is not valid for that. How do I send data and commands to the server after inital connection?

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