I spent a lot of time figuring out how recurring payments actually work in PayPal, and I finally have a pretty good mental model of it. If you're trying to set this up and are exhausted going through their docs, here's the whole picture in one place.

The short version of what finally made it click:

With Reference Transactions, you control the subscription. You hold the token and decide the amount and schedule of every charge.

With the Subscriptions API, PayPal controls it. You define a plan, the customer subscribes, and PayPal runs the billing on its own schedule.

Full breakdown here