Why do you need to sign an event saying paid?
Discussion
You cannot enforce the fee otherwise
how about lnurl-withdraw or cashu sent with the video?
Cashu may as well be a signed event, like zaps.
LNURLW is not proof (it is an offer to pay, not proof of payment)
Isnt a directly taken "offer to pay" a proof? What do I dont see in the context?
Or you mean you need the proof for "accounting" purposes?