The Invalid Cost Centre Set Up for Essential Plan Alert (Modal) was added in Version 3.5.0 (Commercial) as Cost Centres (e-Cost) are now included in the Essential Plan, allowing you to add one Primary Cost Centre.

The above Modal is displayed when the Plan Level is Essential and e-Cost is selected from the side menu when there is more than one (1) active Cost Centre.

To resolve this alert, either Change your Plan Level from Essential to Advanced or Delete a Cost Centre.