UPS/FedEx are domestic only. Most others do allow international although Atlas had international jumpseats blocked for covid and unsure if they started allowing it again. Biggest hurtles are finding out what the schedule is (not always published but FDX, UPS, GTI, WGN are), how to list (ALPA App), and where to meet the aircraft/crew (good luck?). I can tell you from experience that, if you can figure it all out, 13 hours on the top deck of a 74 is a million times better than stuck in a middle seat on AAL/DAL/UAL. WGN was awesome because, after you are approved, the Captain gets your contact info and will get in touch with you directly about meeting location/time. I made the mistake of bringing food because I wasn't sure about the catering situation...I swear they had that plane catered for a king.