A “Write off” invoice creates a credit note as an adjustment against the invoice. In order to void an invoice that has been written off, you should remove the adjustment credit note linked to it before you can void it. Follow the steps as described below.
Go to the Adjustment Credits section of the invoice that was written off
Click “...” to the right and select Remove
Check for the change in the Invoice status and click Confirm
Now go to the Invoice section and select “Void the invoice”
Here’s a video on the above. To regenerate a voided invoice refer to this article.
Note: When an invoice is written off, an adjustment credit note is created for the invoice value which reflects under bad debt. Once you remove the adjustment credit note, the amount will be reversed and recorded under the "bad debt reversal" column of the account summary report
Related articles and Documentation
Where can I see the details for bad debt?