What if we make a new tag for notes called zap_required or something? When a user posts a note, they can request a minimum zap amount in order to reply on the note. When rendering the note, clients can filter out any replies that haven’t zapped the OP the minimum requested amount. nostr:note16p2f5mhtal7lped259rrtzp09dy7aew22j4kkzzfxxl4qejdqcvq3q5d72