How to check unitpay digital signature?

Question

PHP

I connect unitpay to my site.
I opened the documentation: https://help.unitpay.ru/article/31-creating-paymen...
It says that you just need to redirect the user to their url with GET parameters. I did not find a way to attach a handler here -> I conclude that this is just a payment, although you can pass a digital signature in GET parameters, but how can you check it later without a handler?
I found the "payment processor" field in the unitpay control panel, but I didn't understand everything at
all
.
Explain a little please

Answer 1

Well... a peculiar system...
The handler is a script on the side of the store, to which the payment gateway sends notifications about changes. the corresponding request. The request to the handler may contain a digital signature, which should be checked so that no malicious person sends false notifications (if he knows where to throw, but does not know the secret key).
And to start the payment, in theory, you yourself on your side with a script can calculate the signature for the request, generate a URL with this signature and return it to the user under a redirect.