"Pay once" is sustainable as long as people keep buying your app. Which works out just fine, since you are never going to saturate the market as a small app dev

"Pay once" is sustainable as long as people keep buying your app. Which works out just fine, since you are never going to saturate the market as a small app developer. There's always going to be new people who buy your app. I've made a living from non-subscription app sales for a decade, and revenue is pretty constant. As long as your app stays useful, people will continue to buy it.