I was getting the error: “Word cannot register your account. The provider where you are trying to publish is unavailable. Contact your provider for assistance.”
This was caused by me forgetting to add ” /xmlrpc.php” to the end of the url.
So if you want to register a blog “https://my.blog.com” in Word 2016, then you should use the url “https://my.blog.com/xmlrpc.php ”