You can see in a supplier file if a supplier is connected to the Peppol network. Please note: the Peppol badge will only appear after you've received an invoice from this supplier (imported and processed in fast input).
Is your supplier connected to Peppol but you haven't received a Peppol invoice yet? Then you will see a button to ask your supplier to send any new invoice via Peppol from now on. The button will send an email to your supplier (to the first email address in the supplier file) and the button will turn grey. As soon as the supplier sends their next invoice via Peppol the button will turn into a Peppol badge. If the next invoices arrives via email or post the button will turn green again and you can send another email asking to use Peppol in the future.