BR-KSA-28
If the cryptographic stamp (KSA-15) exists in the invoice, this cryptographic stamp (KSA-15) must contain the exact "urn:oasis:names:specification:ubl:signature:1" value for signature information ID.
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.
cac:AdditionalDocumentReference/cac:Attachment
exists(cbc:EmbeddedDocumentBinaryObject) and (cbc:EmbeddedDocumentBinaryObject) != '' and (//ext:UBLExtensions/ext:UBLExtension/ext:ExtensionContent/sig:UBLDocumentSignatures/sac:SignatureInformation/cbc:ID) = 'urn:oasis:names:specification:ubl:signature:1'
Checked with Saudi Arabia ZATCA Tax Invoice (UBL), Saudi Arabia ZATCA Simplified Tax Invoice (UBL)