A refund couldn't be posted because the Xero account isn't enabled for payments
The credit note was created in Xero successfully - it is only the refund payment that was rejected. Xero will not accept a payment into an account that hasn't been enabled for payments.
In Xero, open the account mapped for this refund - usually the gift card / store credit account, or the payment gateway's bank account - and tick Enable payments to this account.
Once the account is enabled, re-post the order from Dashboard - Orders. Nothing re-tries it on its own — enabling the account in Xero isn't something the app can see, so the order waits until you post it again.
Re-posting won't create a second credit note. The one already in Xero is updated in place and the refund payment is applied to it.
Still stuck? Email us at help@hyvelabs.co with your shop URL, the order number and the message shown on the order.