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PEPPOL-EN16931-R110BT-134
input
A line period starts before the invoicing period
`Invoice line period start date` (BT-134) must fall within the invoicing period declared in the header (BT-73).
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
A line that runs outside the announced period casts doubt on which accounting period the invoice belongs to — exactly what a tax audit looks at. The classic case is a service trued-up over an earlier month, left inside a monthly invoice.
How to fix it
Widen the header period, or move the line onto a separate invoice. Factlint changes neither date: nothing says which one is wrong.