Hello Delicious-Nothing,
Using this api link:
https://my.uscis.gov/secure-messaging/api/case-service/receipt_info/IOExxxxxxxxxx
Have you ever seen this response? This is for the I-751. Stiil waiting 12 months now for interview, but I think there's a problem with the I-751 receipt_info not being assigned a field office.
{"data":null}
When I use it for the N-400, data comes back.