When you work with the SEPA downloads, you can process the results in our system.
Normally, if a client reverses a payment immediately when you try withdrawing it, you can process this reversal in the SEPA results with a certain error code. The invoice will automatically be set back to outstanding so you can try again in the next batch.
Since your clients have quite some time to reverse a payment you've tried withdrawing from your account, you might have already put their invoice to "paid" when the reversal comes through.
When you want to process a reversal after the invoice is put on paid, you can go into the invoice and delete the payment there. Just click the trash can next to the direct debit payment, and you will see the invoice will be set back to outstanding. Unfortunately, you will not be able to see in the invoice that it was reversed, it will just look like an ordinary outstanding invoice.
In the future we would like to develop a button that says "reversal" so you can easily process it and it will show in the invoice.