E-invoicing has been mandatory in Italy too for a while. The rollout started in 2014, but it took years to complete. The main integration system is based on the exchange of XML files via SFTP.

So sending an invoice means leaving an XML file in a folder, then polling the server and waiting a few hours to get a response in the form of another XML file in another folder.

You can also integrate via web service, but I think SFTP is still the most popular method, especially for its batching capabilities.