Lexware Office, previously known as lexoffice, is one of the most widely used online accounting packages in Germany. If you cater in the German market, or your accountant is based there, chances are your books already live in it.
Connect Catermonkey to Lexware Office and a Lexware button turns up when you edit an invoice. One click sends the invoice across, VAT breakdown included, ready to be booked. Nothing gets retyped, and no invoice goes missing between the two systems.
You switch the connection on under Settings › Integrations and sign in once with your Lexware account to confirm it. If the button stops showing up later, check whether that permission is still valid. That's usually what's behind it.