Cost element & can only be used for activity input

What causes this issue?

You have defined cost element &V1& in the planning layout or entered it
on the planning initial screen.
This cost element has type 43 and is thus used for internal activity
allocation or for activity input in plan.
In your planning layout, however, the activity input is either not
supported by a different sender cost center or
no values have been entered for the sender cost center and the sender
activity type,
so that cost elements with this type can not be considered.

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

System Response

Cost element &V1& is not allowed.

How to fix this error?

Remove the cost elements with the above type by changing the planning
layout or by not entering cost elements with this type on the planning
initial screen, or
Use a planning layout that is supported for activity input planning.

Error message extract from SAP system. Copyright SAP SE.