#1. Have a free version, that free version has 10 ad slots, and ads cycle with each notification, creating value for the advertiser, but not straining the user with one single advertiser every day.
#2. Have a paid version, $9.99 per year is nothing for a bot like this, and this version would be ad free.
#3. Have an enterprise version, $99.99 per year, this one is for the operators and various businesses at the forum, TryNinja I don't know if you remember when I dropped a donation and requested a chat group environment where I would be getting notifications for Coinslotty, that would be a good option to introduce. For a business $99 is nothing, and for you it means improving the product even further.
i would pay for something like this. and i especially agree with the point about adding more ad slots. you can run an auction for the slots, or sell them for a fixed fee.
seeing the same ad on every notification makes me subconsciously ignore it (ad fatigue), and i can imagine it would do more harm to the brand in the long run since no one likes ad spam.
none, i would say, or we would already have had someone do that.