This is direct integration with unlimit payment system, it allows you to manage subscriptions with recurrent payments
Here is the step-by-step guide in English for the Test/Sandbox environment based on the provided images:
Projects -> Project settings -> Payments -> Unlimit
Callback secret-
Unlimit dashboard -> settings -> wallets -> [CLICK YOUR WALLET ID] -> Show credentials -> Callback secret field
Terminal password
Unlimit dashboard -> settings -> wallets -> [CLICK YOUR WALLET ID] -> Show credentials -> Terminal password field
Terminal code
Unlimit dashboard -> settings -> wallets -> Terminal code