Where can I get paymentId from?

Question

Yandex

I'm trying to figure out the Yandex cash register api, it's not clear that https://github.com/yandex-money/yandex-money-joinu...
it says "When creating a payment in the return_url parameter, you pass a link that will work at any stage of the payment as a link of the "return to the store" button. When the payer goes to your return_url page, we recommend that you query the status of the payment." I understand it this way, there is a return_url to which the user will be redirected after payment or not payment, and I can find out the payment status from this address in the code, right? But how ? Where can I get paymentId from? Does the API send at least some data to return_url or just redirect ? In general, after the user has moved to return_url, how can I collect information about the payment?