Message

If the VAT accounting currency code (BT-6) is present, then the Invoice total VAT amount in accounting currency (BT-111) shall be provided.

Context
/ubl:Invoice | /cn:CreditNote
Test
every $taxcurrency in cbc:TaxCurrencyCode satisfies exists(//cac:TaxTotal/cbc:TaxAmount[@currencyID=$taxcurrency])
Usage
/ ubl:Invoice / cac:TaxTotal / cbc:TaxAmount
/ ubl:CreditNote / cac:TaxTotal / cbc:TaxAmount