I used to work in finance and this is what really happens when you use buy now, pay later apps

Buy now, pay later (BNPL) is great. It only takes a minute to set up your account on the app, and there you go. You can afford the nice stuff you want, because you can pay for it over four months. As long as you keep up the payments, it is an easy, interest-free loan. This is true.

Source : https://www.pocket-lint.com/buy-now-pay-later-is-quick-and-easy-but-part-of-the-system/