The payment instructions are missing
An XRechnung invoice must carry the `PAYMENT INSTRUCTIONS` group (BG-16), so at minimum the payment means type code (BT-81).
Only the issuer holds this value: Factlint reports it and never fabricates it. Test your invoice to find out whether it is affected.
Why this error happens
EN 16931 leaves this group optional; the German CIUS requires it. A generator tuned for another country therefore produces XML that is perfectly valid in European terms and refused by a German recipient. It is the most common gap on a first move to XRechnung, because it comes from an extra requirement rather than from a mistake.
How to fix it
Fill the payment means in from your invoicing system. Factlint writes no payment details, not even partial ones: it is a financial field, and the policy refuses it whatever is asked (rule 1).