PEPPOL-EN16931-R055: Invoice total VAT amount and Invoice total VAT amount in accounting currency MUST have…

The rule applies to UBL Invoice and CreditNote. It checks that if cbc:TaxCurrencyCode is present, the VAT total amounts reported with @currencyID equal to cbc:TaxCurrencyCode and with @currencyID equal to cbc:DocumentCurrencyCode are both less than or equal to 0, or both greater than or equal to 0. A zero amount is allowed with either non-negative or non-positive values, but one positive and one negative amount fail. The document passes if no cbc:TaxCurrencyCode is given.

Compare the two cac:TaxTotal/cbc:TaxAmount values: the one whose @currencyID equals cbc:TaxCurrencyCode and the one whose @currencyID equals cbc:DocumentCurrencyCode. Ensure both values are <=0 or both are >=0, i.e. not one positive and one negative. Correct the sign of one of the amounts accordingly. If a tax currency code is not actually applicable, removing cbc:TaxCurrencyCode also satisfies this rule, but check that this does not conflict with other requirements.