Hi Stanley,
Can you check that the collaboration window Invoice Scanning Settings are correct? Specifically that the "Only upload PDF files" option is not selected and that only the "Enable service Scanned Invoices" is selected?
Mandatory fields to be present in .txt file are: PO Number, Invoice Date & Invoice ID.
If any of the above fields are missing, SI will not get created with status ‘Ready for posting’.
Hope this helps.
Regards,
Sandeep