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.
The message your validator prints
Copied verbatim from the sealed artefact: this is the exact sentence the check prints when this rule fails.
Start date of line period MUST be within invoice period.
Quoted from schematron-xrechnung 3.0.2, licensed under Apache-2.0.
Common searches around this code
These phrases mirror what an integrator searches for: code, syntax, rule, business field and correction.
Test your file with this error in mind
Upload the invoice involved: the report will say whether this code appears, where it appears in the document, and whether Factlint can only report it or also fix it.
To automate this check in an ERP flow, call the validation API and link every returned code to its public page.
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.
XML correction example
ligne : <ram:StartDateTime>20260401</ram:StartDateTime> (facture : 20260501)
ligne : <ram:StartDateTime>20260501</ram:StartDateTime>