IssuerAssignedID exactly once

Error FX-SCH-A-000615 Factur-X

Element 'ram:IssuerAssignedID' must occur exactly 1 times.

Mandatory rule: As long as it is violated, the invoice is invalid and will be rejected by validators.
What is wrong

ram:AdditionalReferencedDocument does not contain exactly one ram:IssuerAssignedID. The element is either missing or occurs more than once.

What the rule means

ram:IssuerAssignedID contains the identifier assigned to the referenced document by its issuer. Exactly one occurrence is required for this document reference.

Please provide exactly one IssuerAssignedID

The issuer-assigned identifier is missing from ram:AdditionalReferencedDocument or appears more than once. This document reference requires exactly one ram:IssuerAssignedID.

What to do
  1. Locate the affected ram:AdditionalReferencedDocument in the invoice line’s settlement.
  2. Make sure it contains exactly one ram:IssuerAssignedID.
  3. Generate the invoice again and check it once more.
What it looks like
✗ Triggers the message 
<ram:AdditionalReferencedDocument/>
✓ Correct 
<ram:AdditionalReferencedDocument>
  <ram:IssuerAssignedID>REF-1</ram:IssuerAssignedID>
</ram:AdditionalReferencedDocument>
Technical details

The test counts direct ram:IssuerAssignedID elements within ram:AdditionalReferencedDocument and requires exactly one.

Where the rule applies

The rule applies within ram:AdditionalReferencedDocument in the settlement for an invoice line.

Context (rule/@context)
/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:IncludedSupplyChainTradeLineItem/ ram:SpecifiedLineTradeSettlement/ram:AdditionalReferencedDocument
Test expression (assert/@test)
count(ram:IssuerAssignedID)=1