PROBLEM IN SHORT: 

When i try to import Excel files which incl. fields "invoice_line_ids/is_refund" or "invoice_line_ids/move_type" i get Error Import preview failed due to: 'model_name' 

More COMPLETE:

I use odoo 18 online in germany.

I want to import lists with invoices (invoice lines). A way like in the video at the End of my posting seems to work for me. I have tried import successfully.

But my lists also include refunds (reversed invoices or credit notes ).

To find out, how credit notes are marked in the database, i made a credit note from an invoice on the GUI and exported it with a lot of possible invoice_line_ids fields. I found the fields "invoice_line_ids/is_refund" (values are boolean) and "invoice_line_ids/move_type" (values are 'out_refund' or 'out_invoice') deal with refunds.

But when i try to import excel tables which have one of these fields included i get an Error:

Import preview failed due to: 'model_name'

To find the reason i also reduced my export only to 1 field "invoice_line_ids/move_type" (with the import hug set). When i try to reimport these unchanged export Excel file i get the same error!

What is wrong with this?

Or how can i import credit notes / refunds?

Here the Video from Cybrosys Technologies, how to import invoices in bulk :