Hi been at this all night, now time to ask the wise!
What is wrong with this?!
I have set privileges to everything for POST GETS, API and SCRIPTS. The idea is to add some data to an external database when a user registers. The JSON works in the API docs (so the fields are right) but not as a pre or post POST. hiyer is the MySQL service name and the registration in the DF Users section are being added fine for both pre and post post.