Install the payment system Robokass at auction

You need to integrate the Robokass payment system into the auction script Testo nascosto.
The principle of payment acceptance: the User in his personal account, presses the button "to replenish the balance of the account" It gets into the Robokass payment system. Pays any amount. After successful payment, he has a paid amount in his account.
You just need to integrate the form into the script. You don't have to tune in.
On the website of Robokassa there is a detailed description of how to install a payment button on any site.