@jmanuelortiz we moved configuration to wrapper-properties.conf as of 19.6. From the issue you posted:
The agent will no longer honor the GO_SERVER_URL environment. This environment variable will be removed upon upgrade.
If the file config/wrapper-properties.conf exists, you must add the following config options to that file (substituting the appropriate GoCD server URL).
Otherwise it mimics the GitHub payload body well enough (we only check for the ref and repository chunks), as well as x-GitHub-event.
But the auth is wrong.