# CII-SR-456

Source: https://xmlvalid.com/rules/CII-SR-456

> DefinedTradeContact of BuyerTradeParty shall exist maximum once

- Level: error
- Rule sets: EN 16931 rules (CII) 1.3.17, EN 16931 rules 1.3.16 (CII), EXTENDED-CTC-FR rules (CII) 1.4.0.04
- Context: `/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement`
- Test: `( count(ram:BuyerTradeParty/ram:DefinedTradeContact) <= 1)`

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