So we are doing an App Extender conversion, using the same code to login to the API we'd used a thousand times before, and I get a login error, "Error sending HTTP request to server".

Ok fine, I build a little app to login to the server - that's all it does - and it works fine using either WA or a repo account.

Port it to the remote location and all is good. It works both ways.  I take the same dlls (10.4) set the dot net version to the same value (4.7.2 or 4.8) and drop the EXACT SAME CODE into the migration app, using the exact same references.  And get the same error,  "Error sending HTTP request to server".

So one app works the way we want and another does not, using the exact same dlls, references, .net version and code.

Has anyone else seen this weirdness?