You cannot delete key figure &

What causes this issue?

Data for the planning area already exists. You are not allowed to
subsequently remove time series key figures.

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

System Response

How to fix this error?

If you wish to remove the key figure, you will first have to delete all
existing time series of this panning area (de-initialization).

Error message extract from SAP system. Copyright SAP SE.