What it means
The payment and VAT section of the invoice (ApplicableHeaderTradeSettlement) must not contain ProFormaInvoiceReferencedDocument, a reference to a pro forma invoice, which is a preliminary invoice sent before the final one. EN 16931 has no field for it.
Why it matters
This rule is a warning, so the file is still accepted. The reference is outside the standard, so the recipient's software is not expected to read it and the number is likely to be ignored.
How to fix it
Remove the reference by choosing the EN 16931 option in the e-invoice export of your invoicing software, or by deleting the element if you create the XML yourself. If the buyer needs the pro forma number, mention it in an invoice note (BT-22).
The rule as published
ProFormaInvoiceReferencedDocument should not be present Where this rule applies
| Rule set | Version |
|---|---|
| EN 16931 (CII) | 1.3.17 |
| XRechnung 3.0 (CII) | 3.0.2 |
| NLCIUS (CII) | 1.0.3.13 |
| France CTC (CII) | 1.4.0-04 |
Check your file
Drop your e-invoice to see whether CII-SR-423 still fails, and which other rules do.