Isnít a Forever USA stamp considered a First Class stamp? My application was returned today and only thing I noticed was the stamp was crossed out with ink. 1A is still showing plenty of licenses.
Are there any barcodes on the outside of the envelope... front or back? Apparently they didn't give a reason for it being returned...which is why you are asking.
Often times when a postal worker finds an envelope with a stamp in the mail stream that isn't canceled, they will draw a line through it voiding it for reuse (revenue protection). That line would not have caused it to be returned.
I'd dot your I's and cross your T's on all the other stuff that has to be correct with the app process. Like filling out all the fields on the app, the envelope, check properly filled out....It wouldn't have rejected because of a Forever Stamp.