# F-INV021

Source: https://xmlvalid.com/rules/F-INV021

> One PaymentExchangeRate class must be present when PaymentCurrencyCode element is used

- Level: error
- Rule sets: OIOUBL 2.1 Invoice rules (Denmark) 1.17.2
- Context: `doc:Invoice/cbc:PaymentCurrencyCode`
- Test: `count(/*/cac:PaymentExchangeRate) != 0`

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