The only serious attempt I’ve seen is https://creatr.nostr.wine . I am not in favor of using paywalls this way, however, so I cannot speak to how effective it has been as I have not tried it. I think nostr:npub1jk9h2jsa8hjmtm9qlcca942473gnyhuynz5rmgve0dlu6hpeazxqc3lqz7 tried it at one time. Maybe he has some insight.