Summary
A transaction already approved (and in some cases captured) receives a cancellation request directly from the checkout:
An external application called to cancel this transaction Id = with Value RequestId = . Priority: default. Author: vtex-service::checkout::stable. This cancellation request occurs due to a timeout when the checkout calls the payments route from the gateway, and the service takes too long to respond.
This happens when the newGatewayCallback method is triggered at two different points in the order flow:
- During the order processing stage – when the endpoint 
gatewayCallback/{orderGroup}is called. - After the payment authorization – when the endpoint 
gatewayCallback/{orderGroup}/{messageCode}is called. 
In both cases, the newGatewayCallback  performs a request to the payment gateway. If the gateway takes too long to respond, the same type of timeout error can occur in either scenario.
To clarify further:
- The first call is a POST request to 
gatewayCallback, which occurs right after the user completes the checkout process. - The second call is a GET request to 
gatewayCallback, which is triggered during payment confirmation – this is when the shopper is redirected to the "Order Placed" screen. 
Simulation
Simulation is not possible.
Workaround
No workaround available.