Invoices are typically sent via Peppol based on the customer's VAT number or business number. This number is used to register the customer on the PEPPOL network, ensuring that invoices are sent to the correct address.

If the customer does not have a VAT number or business number, a specific Peppol number, called a GLN, can be used. This GLN number is a unique code that identifies the customer in the Peppol network.

To set up the GLN number for a customer, add it as customer data. Go to "Settings" > "additional fields" and add a new extra field. Choose "GLN (Peppol)" for "Specific meaning" and don't forget to save the custom settings.

After adding the new extra field, you can enter the GLN number in the customer details and send the invoice via Peppol.

Similarly, you can also specify the Dutch Chamber of Commerce number, Dutch OINO, or the Norwegian organization number.