[UBL-SR-12-GST-SG]-Seller GST identifier shall occur maximum once
UBL-SR-12-GST-SG
/ubl:Invoice | /cn:CreditNote
(count(cac:AccountingSupplierParty/cac:Party/cac:PartyTaxScheme[cac:TaxScheme/cbc:ID='GST']/cbc:CompanyID) <= 1)