Mockserver fails to match expectation for received message
Solution 1:
It looks like in your test you are creating the expectations in MockServer after executing the call to your code under test? The fact that your console output from MockServer does not output matched/not matched expectations (the default behavior) indicated to me that there are no expectations setup when the web request is made to MockServer and a 404 is default response by MockServer when there is no expectation for a request.
Try adding that expectation as the first line in your test.