Let me share some details about the error when attaching a PDF file to an invoice.
Currently, there are reports of files not attaching, and the engineering team is aware of it and hope to have more information soon. In the meantime, you can try removing the extra space before the extension. The file name should look like this "filename.pdf".
Find and open the desired invoice.
From the bottom left, select Attachments.
Browse and select the document you want to attach.