When you do a search for running the 3038e PTO with an empty seat, this is the top search hit so I thought I would update it since I had the same problem. I have a 2019 3038e and the manual I received clearly states you must be in the seat to operate the PTO, but this is incorrect.
Sit in the seat and start the tractor.
Make sure it is in Neutral and the parking brake is On.
Leave the seat and then turn on the PTO. It and the tractor will continue to run.
If you start the PTO while still seated, and then leave the seat, the seat safety switch will kill the tractor.