I don't know, which one is it?
I am worried that it might be one of the OTHER places where 173 is being returned. Such as if Apple's Root CA is missing.
I thought that whole /receipt thing as autogenerated by apple.
Apple signs with their own certificate when posting on the MacOS store. We were checking for OUR own certificate (the one we used to sign when submitting to Apple.)
http://grab.by/9gmN This is the only clue I have.