Transaction canceled by timeout, checking the logs in Splunk you can see the following message:

exception_type=Vtex.Commerce.Checkout.Exceptions.CheckoutException exception_message="Timeout no request para o Sistema de Parcelamento" account_id="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" message="Timeout no request para o Sistema de Parcelamento"

In the transaction logs you can see the following message:

An external application called to cancel this transaction Id = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx with Value xxxx RequestId = xxxx-xx-xxTxx:xx:xx-xxxx. Priority: default. Author: vtexappkey-appvtex.

Cannot simulate.

There is no workaround, the transaction is immediately canceled when this happens.