I'm trying to add a field to a form via the REST API (this will eventually be done to hundreds of forms which is why I want to do it via the API) but I get a System Error when I try to set 'fieldType' to 'hidden'. When I run the 'Get Fields For Form' endpoint I see that 'dataType' is 'hidden' for the hidden fields, is the 'fieldType' declaration different (they seem to match on everything else)?
What I'm trying to run that is giving me the system error (personal data XX'd out).
Post Payload: fieldId=myField__c&label=HiddenFieldLabel&fieldType=hidden&access_token=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX:XX
Also, is there any documentation on how to set the Autofill settings for hidden fields via the API?