Material-routing assignment already exists in the future

What causes this issue?

You want to create a material-routing assignment, however, the
material- routing assignment already exists. The valid-from date for
the material- routing assignment is later than the key date you
entered.

System Response

The validity of the material-routing assignment is not extended.

How to fix this error?

If you want to extend the validity of your material-routing assignment,
proceed as follows:
Enter a key date (or a change number with a key date) that is within
the validity period of the existing material-routing assignment.
Delete the existing material-routing assignment.
Enter the key date from which you want the material-routing assignment
to be valid.
Create the material-routing assignment with this key date.

Error message extract from SAP system. Copyright SAP SE.