Maintain default cost element in controlling area &

What causes this issue?

CO down payment update is active in controlling area &V1&. You must
therefore maintain a default cost element and a default revenue element
for down payments.

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?

Maintain the default cost elements for down payments for controlling
area &V1& in the Project System implementation guide.
<DS:SIMG.SIMG_OLPR_OKEP>More information</>

Error message extract from SAP system. Copyright SAP SE.