PEPPOL-EN16931-R043: An allowance or charge's indicator flag does not have the value…
What it means
An allowance or charge's indicator flag does not have the value 'true' or 'false' exactly, so software cannot tell whether it is a charge or an allowance.
How to fix it
Set the ChargeIndicator to the literal value 'true' (charge) or 'false' (allowance).