I understand that you there may be some pressure to comply with the new German legislation as soon as possible, but if I understand correctly from the following online article (in EN, DE), there is only an acceptance obligation for b2b transactions.
Moreover, paper and other e-invoices that do not meet the standards can still be exchanged until 31/12/2026.
The focus is therefore currently only on being able to receive (and understand the content) of the e-invoice when you receive it.
This gives you at least 2 years to adapt to these obligations…
InvoicePlane is an application that sends invoices (in PDF format) to customers.
Currently, there is no possibility in IP to receive (e)-invoices.
My advice is to look for a (freeware?) UBL/Xrechnung viewer (QUBA-viewer?), so that you can view the (few) e-invoices that you may receive.
i only find application/libraries/zugferdxml.php ?
UnderDog refers to a Pull Request that is still in development at the moment…
The file you refer to generates Zugferd V1.0 files and is very outdated.
If Zugferd is activated (via Settings - Invoices) in the current IP version, all your invoices will be sent with a Zugferd V1.0 XML embedded in the pdf files.