# F-INV027

Source: https://xmlvalid.com/rules/F-INV027

> Invalid Signature/ID. Must contain a value

- Level: error
- Rule sets: OIOUBL 2.1 Invoice rules (Denmark) 1.17.2
- Context: `doc:Invoice/cac:Signature`
- Test: `normalize-space(cbc:ID) != ''`

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