If you have accidentally linked an invoice as an attachment, while it should not have been an attachment, this cannot be undone. The invoice has been converted into an attachment and will not go through the workflow steps of ISP-Invoice. You can scan the invoice again or e-mail it to your version of ISP-Invoice. In this way, the invoice is seen as new and you can still process the invoice.
You can delete the attachment that you have linked to another invoice.
More information
All frequently asked questions are listed in the section FAQ.