Depending on how outgoing invoices have been implemented so far, there are different implementation possibilities:
Do you use a service provider or commercially available software for invoicing? Contact the manufacturer and find out whether electronic invoicing is supported.
Do you use your own system? Clarify with your IT department which steps are necessary to create e-invoices in compliance with EU standard 16931 and the German legal situation. The currently valid version of the complete documentation of the standard is available on the KoSIT website.
If you are not using an outgoing invoice system or if you need an interim solution, familiarise yourself with the ZRE/OZG-RE web-based entry system.