Anything unexpected returns 503. Try <a href="http:&#x2F;&#x2F;codes.io&#x2F;404&#x2F;" rel="nofollow">http:&#x2F;&#x2F;codes.io&#x2F;404&#x2F;</a> (notice the ending &#x2F;)<p>Besides, 1223 isn&#x27;t specified by the HTTP RFCs, nor is it returned anywhere except from a library call in a buggy library. I&#x27;d say it&#x27;s not appropriate for an HTTP testing service to support 1223.