Don't you have a registration form? When a guest checks in, the hotel should ask the guest to fill in a check-in registration form, which is fine, and the valid seal of the hotel can also be used.
If you are writing on a typewriter, you can.
Write the title: proof of occupancy
This is to certify that Mr XXX has stayed in this hotel for a certain period of time, and that the year, month and day are valid seals of the hotel.