I don’t know what the issue is. The message isn’t actually an error, but a success message which should be received in the background. You would only see it this way if there was some other problem. I can’t make guesses, but it suggests a server misconfiguration or some other component interfering with returned data.
I can’t debug this for you, or suggest a fix. As a “layperson” your only option is to contact your hosting support, but – based on my experience – they are very unlikely to do anything other than send you back here.