When canceling a payment, API_Callback is not called. How to be?

Question

Classmates

We call showPayment, if for some reason the payment failed, then API_Callback is not called, although judging by the documentation it should be called with the "cancel" parameter. We tested it like this: showPayment is called, while the user does not have OK on the account, and in the account replenishment window they clicked cancel.
The second question has already been asked here: https://toster.ru/q/227538, but the problem remains and how to deal with it is not clear: if, after a successful purchase, the user clicks on the cross at the top right of the successful purchase window, then API_Callback with the ok parameter will not be called. The same problem with other windows (at least the FAPI.UI.showNotification window) - if you click on the cross, there will be no notification.
The first question is more important!

Answer 1

No way. Check with requests to your server.
How to handle the closing of the notification window, invitations, etc.?