I am getting back a 404 Cannot POST /v1/authorization error suggesting that that endpoint doesn’t even exist? Though it matches what is on the spec https://volt.build/api-spec/
Looking over the logs, I found several requests with the parameters concatenated on to the URL (e.g. http://example.com/path? grant_type=client_credentials&client_id=xyz&client_secret=abc). You are correct that the proper request should be x-www-form-encoded (as the OAuth2 spec states).
However this isn’t the main issue - it looks like the endpoint you’re using is incorrect. I see several requests to /v1/authorization when the proper endpoint is /v1/authenticate. Give that a try and see if it works.