Specification key & outside of permitted range

What causes this issue?

You entered a specification key that is not within the permitted
interval.

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?

Enter a different specification key that lies within the permitted
interval.
Instead, you can also let the system assign a specification key by
leaving the specification key field blank.

Error message extract from SAP system. Copyright SAP SE.