# GR-R-008-3

Source: https://xmlvalid.com/rules/GR-R-008-3

> When Supplier is Greek and the INVOICE URL Document reference exists, the External Reference URI should be present

- Level: error
- Rule sets: Peppol BIS Billing 3.0 rules 3.0.21
- Context: `cac:AdditionalDocumentReference[$isGreekSender and cbc:DocumentDescription = '##INVOICE|URL##']`
- Test: `string-length(normalize-space(cac:Attachment/cac:ExternalReference/cbc:URI))>0`

Validate a document against these rules: https://xmlvalid.com/validate