OTM Invoice Upload CSV

I have the following requirement. The service provider sends an invoice as a CSV file. I would like to upload this file to OTM so that an invoice validation can take place. The invoice is matched to the shipment using a reference number. I have downloaded the invoice CSV file from OTM, but for the upload to work I have to download several CSV files with the relevant table names, e.g. Invoice_Refnum.

Is there a simpler solution? In this case, the service provider is not integrated with OTM.