Enter activity type only in conjunction with cost center

What causes this issue?

You have specified an <DS:DE.LSTAR>activity_type</> as an account
assignment object without the corresponding
<DS:DE.KOSTL>cost_center</>.

System Response

You can only specify an activity type together with a cost center.

How to fix this error?

Delete the account assignment for the activity type or enter a cost
center.

Error message extract from SAP system. Copyright SAP SE.