How to automatically fill in details in online banks?

Question

API

On some sites (For example: https://service.nalog.ru/gp2.do) , when choosing a non-cash payment through Sberbank, payment details are automatically filled in. (TIN, purpose of payment, account number) All that remains for me to do is click the pay button and that's it. No need to manually enter all the data from the payment order.
I can't find anywhere how it's done. I did not find an API from Sberbank.
How can I automatically fill in the details from payment orders?
How to reproduce:
Step 1: fill in the data on the site (full name, TIN) and select Sberbank

Step 2: log in to Sberbank

Step 3: see the completed details

Answer 1

I could not reach the step where something automatically filled in for me.
Please attach screenshots with steps.
Again, Sberbank and public services can be mutually integrated by non-public methods :)