Depending on the file type of the invoice images, you can add more images in the invoice log. For example, if you have your invoices in PNG or TIF format, you can add additional pages, but if the invoice is a PDF file, you can't.
In order to add additional pages to an invoice, they must be in the same format as the original images for the invoice. In other words, only other files in PNG format can be attached to a scanned invoice in PNG format.
If you want to add a PDF file to an invoice, it has to be done under Comments after the invoice has been transferred from the invoice log.