BR-FXEXT-01
If the Invoice Free Text subject Code (BT-21) is specified, either the coded message free text (BT-X-5) or the message free text (BT-22) must be specified, or both. If both BT-X-5 and BT-22 are specified, both must have the same meaning.
error: the document is invalid
What the rule checks
As the rule set's publisher wrote it. The rule runs on every element the context matches, and fails where the test is false; the validator reports the line of that element.
Context
/rsm:CrossIndustryInvoice/rsm:ExchangedDocument/ram:IncludedNote[ram:SubjectCode]
Test
(ram:ContentCode) or (ram:Content)
Checked with France Factur-X EXTENDED, Factur-X / ZUGFeRD EXTENDED