The planning basis for algorithm &2 is not maintained in model mix &1

What causes this issue?

In Customizing for Model Mix Planning, the planning basis for the
specified procedure has not been maintained for the specified model
mix.

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?

In Customizing for Model Mix Planning, in the IMG Activity
<DS:SIMG.APO_PPS_MMP_MM>Define Procedure Packages</>, maintain a
planning basis for the procedure in the procedure package in question.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.