Content publishers wanted - video/tube sites, browser game portals, file exchange portals etc, both adult and mainstream. We provide you with content lock script that prevents visitors from accessing particular content on your site (by html object id) until the subscription is confirmed. Visitors don't have to pay anything - they just agree to receive push notifications. See the payout rates here: https://tubecorporate.com/home/rates#push_traffic
I tried this content-locking for my fashion site. It totally flopped. I suppose very few can be bothered to opt-in in exchange for notifications.