Many apps in AppStore/PlayStore already have in-app-purchases. So it's basically "Shareware" (a 1990s term) or Lite-version or a demo-version, and to unlock all

Many apps in AppStore/PlayStore already have in-app-purchases. So it's basically "Shareware" (a 1990s term) or Lite-version or a demo-version, and to unlock all features you have to pay once or per year. The difference for the developer is you have to maintain only one version with optional features, and not two different app-versions (demo/lite/trial + full version (maybe even with optional features))