I'm not a native speaker as well, maybe that causes the problem :D I meant the following: customers -> group of people who buy or subscribe to your application

I'm not a native speaker as well, maybe that causes the problem :D I meant the following: customers -> group of people who buy or subscribe to your application, preferably via the App Store, Google Play or some other in-between party. Usually no contract involved. Paying client -> a single person or business that pays you to develop software, probably with a contract that is signed and specifies what you're going to build, on which timeline, etc.