Confused as to why the post request works using the Http Web Request but not with the HTTP Form POST.
When I try to do this it fails.
It looks like it is failing because the API is expecting JSON content. Note how Web Request is sending "application/json" and a Form Post is multipart/form-data.
The error message says "Failed to decode JSON object" which suggests it wants application/json content, rather than the multipart/form-data sent in a form submission.
Is there a reason you want to use Form Post? Basically, that is only useful for posting data to a form (i.e., a web form with named input elements), not APIs that expect JSON, XML, etc.
Oversimplifying a bit, but a Form Post is basically like a user submitting an HTML form object in a browser and that's not what most APIs usually expect.
UPDATE: What Brian said lol