1- The customer should be able to add funds via voucher system (Redeem Voucher)
2- The payment gateway should be on separate server/domain. For example,
2.1- Store is on Server A and there is another Server B.
2.2- Customer comes to store on Server A. Wants to add funds using perfect money.
2.3- Customer inserts the amount he wants to fund his account. Presses button PAY.
2.4- Server A takes that post data to Server B.
3.5- Server B sends that post data to Perfect Money Server using API. Fetches the result and sends back to Server A and add funds to that account if transaction is completed.
REMEMBER: Perfect Money is very strict about payments. There should not be any kind of direct involvement or communication with Server A & Perfect Money Server.