@CGC MikeI was able to find a solution. Once you get the error upon final submission, go back in and edit the first zip code (sending from) to be nine digits with no dash and no spaces. Uncheck the box that makes the second zip code (return to) the same and simply add the dash to only that zip code. The red text about it needing to be 10 characters max still appears, but the submission successfully processes. For the prepaid label, the system generates your address using only the first five digits of the zip code, so the FedEx system will still be able to process. I hope this helps everyone.
