The response you received indicates that the supplier (accounting_supplier_party) and the customer (accounting_customer_party) have not been set up properly for invoice transmission.
To successfully transmit an invoice on behalf of a supplier, the supplier must have selected you as their Access Point Provider (APP). Without this authorization, you will not be able to transmit invoices on their behalf.
To verify the list of businesses that have attached your APP, call the designated endpoint(SearchEntity) to retrieve this information. Ensure that the supplier has properly configured their APP settings in the e-Invoicing system before attempting transmission again.
