Document & ignored for transfer to GTS

What causes this issue?

The system cannot transfer the document because the Intrastat-relevant
status is <LS>Error During Data Transfer for Intrastat</>. The status
was set when the system failed to transfer the document the last time
the report was run to transfer Settlement Management documents because
mandatory data such as <LS>Declaration Date</> (the posting date) was
missing in the Settlement Management document.

System Response

The system cannot transfer the document to SAP Global Trade Services
(GTS).

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.