GR-R-008-2: When Supplier is Greek, there should be no more than one invoice url

This fatal Peppol rule applies to UBL invoices and credit notes where the supplier country code in cac:AccountingSupplierParty/cac:Party/cac:PostalAddress/cac:Country/cbc:IdentificationCode is 'GR'. The test requires that the number of cac:AdditionalDocumentReference elements with cbc:DocumentDescription exactly equal to '##INVOICE|URL##' is either 0 or 1, i.e. no more than one invoice URL. A document fails if it contains two or more such AdditionalDocumentReference elements. Note: the variable $isGreekSender also considers 'EL' as Greek, but the applies-to condition still requires the country code to be 'GR' in that same path, so documents with 'EL' are not selected by this rule.

Remove cac:AdditionalDocumentReference elements with cbc:DocumentDescription = '##INVOICE|URL##' until only zero or one remains. If an invoice URL is required, keep exactly one; otherwise remove all. In the producing system, ensure the generated XML includes at most one such reference. If the supplier country code is 'EL', the rule as given may not apply because the applies-to condition only checks for 'GR'; verify with the validator whether 'EL' documents are also checked, and if so, apply the same count restriction.