Need to finalize payment php script

Good day, there is a script that sends payments in Webmoney and Yandex Money, and after paying all normal returns and payment is credited. But there is a problem that doesnt check keys from both systems , that is, knowing the success of the reverse link can be set off against the payment no charge :) need to modify these flaws :) By WebMoney how to work with secrets I think you already know, Yandex money, people are less likely to face – thats the description – yandex.ru/dev/money/doc/d...