Make it possible for players to pay the game in parts (paying $5.99 for 3-4 times). People are used to paying $5.99, but think $20 is much for casual games. Therefore… let them pay $6 four times (total of $24 minus fees, which takes it close to $20ish profit) and they’ll do it.
Yes, there’s already credit cards that can handle “split payments”, but the psychology of “it’s only $6 per month” is a killer.
Trust me on this.
Or, just try it out for 30 or 60 days and see what happens.