There are various ways of finding out whether customers and/or suppliers are affiliated with Peppol.
Badges will appear next to the names of the customers or suppliers in the customer or supplier records if they are affiliated with Peppol.
When you send an invoice to these customers you will see a green 'Send via Peppol' button.
You can also see in the customer and/or supplier records whether they are affiliated with Peppol.
Please note that the badge will only appear once you have sent your first invoice to a customer or received a first invoice from a supplier (as a pdf, digitally, or imported and processed in the fast input).