FX-SCH-A-000255
An Invoice that contains an Invoice line (BG-25), a Document level allowance (BG-20) or a Document level charge (BG-21) where the VAT category code (BT-151, BT-95 or BT-102) is "Zero rated" shall contain in the VAT breakdown (BG-23) exactly one VAT category code (BT-118) equal with "Zero rated".
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.
[BR-Z-01] An Invoice that contains an Invoice line (BG-25), a Document level allowance (BG-20) or a Document level charge (BG-21) where the VAT category code (BT-151, BT-95 or BT-102) is "Zero rated" shall contain in the VAT breakdown (BG-23) exactly one VAT category code (BT-118) equal with "Zero rated".
/rsm:CrossIndustryInvoice
(count(//ram:ApplicableHeaderTradeSettlement/ram:ApplicableTradeTax[ram:CategoryCode='Z'])=0 and count(//ram:SpecifiedLineTradeSettlement/ram:ApplicableTradeTax[ram:CategoryCode='Z'])=0 and count(//ram:CategoryTradeTax[ram:CategoryCode='Z'])=0) or ( count(//ram:ApplicableHeaderTradeSettlement/ram:ApplicableTradeTax[ram:CategoryCode='Z'])=1 and (exists(//ram:SpecifiedLineTradeSettlement/ram:ApplicableTradeTax[ram:CategoryCode='Z']) or exists(//ram:CategoryTradeTax[ram:CategoryCode='Z'])))
Checked with Factur-X / ZUGFeRD BASIC