BR-AA-10

A VATBReakdown (BG-23) with VAT Category code (BT-118) "Lower rate" shall not have a VAT exemption reason code (BT-121) or VAT exemption reason text (BT-120).   

error: the document is invalid

What the rule checks

As the rule set's publisher wrote it. The rule runs on every element the context matches, and fails where the test is false; the validator reports the line of that element.

Context
cac:TaxTotal/cac:TaxSubtotal/cac:TaxCategory[(normalize-space(cbc:ID) = 'AA' or normalize-space(cbc:ID) = 'RED' or normalize-space(cbc:ID) = 'INT')]
Test
not(cbc:TaxExemptionReason) and not(cbc:TaxExemptionReasonCode)

Checked with Portugal CIUS-PT Invoice (UBL), Portugal CIUS-PT Credit Note (UBL)