Exactly one tax identifier with scheme FC

Error FX-SCH-A-000411 Factur-X

Element 'ram:ID' 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

In this ram:SpecifiedTaxRegistration, ram:ID does not occur exactly once. The element is missing or appears more than once.

What the rule means

A tax registration using scheme FC must contain exactly one identifier.

Please provide exactly one tax identifier using scheme FC

The seller's tax registration using scheme FC is missing ram:ID or contains it more than once. The registration must contain exactly one identifier.

What to do
  1. Find the seller's ram:SpecifiedTaxRegistration whose ram:ID has the value FC in @schemeID.
  2. Make sure this registration contains exactly one ram:ID.
  3. Generate the invoice again and validate it.
What it looks like
✗ Triggers the message 
<ram:SpecifiedTaxRegistration>
  <ram:ID schemeID="FC">123</ram:ID>
  <ram:ID schemeID="FC">456</ram:ID>
</ram:SpecifiedTaxRegistration>
✓ Correct 
<ram:SpecifiedTaxRegistration>
  <ram:ID schemeID="FC">123</ram:ID>
</ram:SpecifiedTaxRegistration>
Technical details

The context selects ram:SpecifiedTaxRegistration using ram:ID/@schemeID="FC"; the test requires exactly one direct ram:ID child element.

Where the rule applies

The rule applies to the seller's ram:SpecifiedTaxRegistration whose ram:ID has the @schemeID value FC.

Context (rule/@context)
/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ ram:SellerTradeParty/ram:SpecifiedTaxRegistration[ram:ID/@schemeID="FC"]
Test expression (assert/@test)
count(ram:ID)=1