When a BIS Invoice or CreditNote message is enveloped, the value of the SBDH element Sender/Identifier SHALL match the Party/EndpointID element value of the sender party, including the value of its schemeID attribute.
/p1:StandardBusinessDocument/p1:StandardBusinessDocumentHeader/p1:Sender/p1:Identifier[$isBilling and not($isSelfBilling)]. = concat(/p1:StandardBusinessDocument/*/cac:AccountingSupplierParty/cac:Party/cbc:EndpointID/@schemeID, ':', normalize-space(/p1:StandardBusinessDocument/*/cac:AccountingSupplierParty/cac:Party/cbc:EndpointID))