[Solved] Error adding a mailbox: The WinRM client sent a request to an HTTP server and got a response saying the requested HTTP URL was not available

I’m getting the following error when trying to add a new mailbox:

Connecting to remote server ___servername___.__example__.com failed with the following error message : The WinRM client sent a request to an HTTP server and got a response saying the requested HTTP URL was not available. This is usually returned by a HTTP server that does not support the WS-Management protocol. For more information, see the about_Remote_Troubleshooting Help topic.