This is because ACH transactions take days to resolve and do not have consistent pre-approval responses between gateways. Stax Bill will not be notified of the status or effect of the refund requested as well.
The request was still sent, but as with other ACH transactions, the status will need to be verified by a user in the gateway account.
If the refund was successful a member of your team will need to issue a corresponding refund as cash, cheque, or direct deposit.