Hello again @boa999
I had asked you above where the file was, but it turns out the software no longer creates a copy of the PDF that is attached. It simply remembers the location of the saved file.
For everyone else who's having trouble with the error "Your transmission didn't go through":
@boa999's solution works. This is a Turbotax Business 2019 bug. To confirm this issue applies to you, click on the "Attachments" icon on the top-right and note the "File Name" field for the "8453 Signature Document" is in fact blank. When you click on the "View" button, if you don't see the file you uploaded, that would confirm that the failure to transmit is stemming from this issue. Apply the above fix, and make sure you can see the name of file you uploaded (in the Attachments window) and that you can see the file itself when you click View.
