Peppol is a network that allows the electronic exchange of various documents, including e-invoices. It requires taxpayers to use services of a Peppol Service Provider, or Peppol Access Point, to exchange documents within the Peppol network (a 4-corner model). Access Points are service providers that can generate, send and process the Peppol BIS format, based on UBL 2.1 or CII.
The main difference between Peppol and the interoperability model is that the exchange mechanism is regulated by Peppol, so service providers can only exchange documents in the Peppol BIS format. Even though invoice exchange via Peppol is mandatory in some countries, (e.g., Sweden, Finland, Norway) it is not considered a CTC model because there are no tax authority controls involved.
Peppol CTC is the upgraded version of the current Peppol 4-corner model. In this CTC model, Peppol Access Points report transaction data to tax authorities or via official platforms in real time. This is a great model to allow both automation for businesses and greater control over the economy for tax authorities.