BoxPay provides various payment methods to allow testing your integration in Sandbox env before you start using Live/Production account. All of these payment methods return a simulated response and don’t call your configured PSPs.
If you wish to do end to end testing, you should refer to specific PSP documentation and use the test payment methods mentioned there.
However if the configured PSP is using same payment method as our test payment method, we will still not be calling PSP and returning our simulated response. For instance, if a card with no 4111 1111 1111 1111 is mentioned as test card for the configured PSP, BoxPay will still return simulated response since it is our test card too. When in doubt, you can always look at the response status.reason field as we always indicate whether the payment was done using BoxPay test card.