Thank you for your post!
I am going to move this thread from the FileMaker Community Feedback Space, which is specifically for input on the Community itself, to the Discussions Space where you should receive more views and potentially more advice!
You can take a look at the example I quickly created.
There are 2 files in there:
StartInvoice, having just one table with invoiceNr and a repeating field holding reptitions which must become portal lines, and
EndInvoice, a file with 2 tables, having an import script which will split the repeating field into portal lines.
Start by opening EndInvoice and clicking on the import button, then on the show invoices one.
FromRepToLineItems.zip 136.3 K
Thanks Siplus, that was fast. I will try that in my solution right away.