Whenever you make a payment on the platform, Request checks if there isn't already a pending decision in your wallet for the same payable. If one is detected, you will see a popup asking you whether or not you'd like to continue with the payment.
The double payment prevention is robust. If you see such a popup and aren't sure which pending decision it is referring to, reach out to our support team for help.
Note that payments made outside of the Request suite are not covered by the protection.