Why is the payment successful for any server response?

Question

Classmates

Actually, why does the purchase in the game take place with absolutely any server response?
For example, neither simply falsenor

<?xml version="1.0" encoding="UTF-8"?>
<error_response>
  <error_code>1001</error_code>
  <error_msg>CALLBACK_INVALID_PAYMENT : Payment is invalid and can not be processed</error_msg>
</error_response>

don't change anything. Anyway, they write off OK from me and show that the payment is successful.