I'm having the same problem using node.js. I can create the parent record entry fine, and I can create the child records fine too, but I can't create the relationship. I have two relationship fields - formID and parentRecordID. In the API call I have:
and the parent_recordID gets filled with 430091 (the form ID) and the form_formID field is left blank, and there's no error reported with the QB API.
Any idea of why this is happening? Or were you able to figure this out?- Rod