Payments. API_callback() not being called or an explanation of how it works?

Question

Classmates

Let's try following the example from https://apiok.ru/wiki/display/api/FAPI.UI.showPaym...
We call FAPI.UI.showPayment("Apple", "This is very tasty!", 777, 1, null, null, "ok", "true");
The payment window appears.
By pressing the Close button or the cross in the upper right corner of the window, API_callback() is not called. In what cases does it even work?
And yet, is it possible to test payments without making real money, is there a sandbox for test applications in which OKs are not debited but emulate a purchase transaction?