What causes this issue?

Declarable substances can not be entered when requirement revision
status is <ZK>Historic</> or <ZK>Released</>

System Response

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

How to fix this error?

If you want to edit declarable substances, you have to first create a
new requirement revision in the status <ZK>In Process </>or <ZK>Not
Relevant</>

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.