Why do they charge 1 ruble when linking a card on marketplaces?

Question

Payment systems

The site has buyers and sellers. The site acts as an intermediary in a secure transaction. After the transfer of the goods to the buyer, the site transfers the money to the seller minus its commission.
Payment to the seller on a bank card.
Question: how to link the seller's card correctly?
Typically, such services write off 1 ruble and then return it. What for? And how to do it right from the point of view of the law and automation of payments?
Sber was supposed to be used as the main acquiring.

Answer 1

1 ruble is deducted for card validation and processing verification. Then they return.

Answer 2

start with Sberbank, there are a lot of things to do right