Sometimes the "Cancel Transaction" icon is engaged, which makes it impossible to cancel the customer refund.
This is the case when the period in which the refund to be reversed is located is subject to a closed bank reconciliation. It is not necessary for the transaction to be selected as part of the period's disbursements in the bank reconciliation to prevent its cancellation. It is sufficient that the bank reconciliation for the period in question is completed and closed to prevent the cancellation of the transaction.
Result:
To make the "Cancel Transaction" icon available again and be able to cancel the customer refund, you will have to open the bank reconciliation of the period in which the refund in question is located.