Down payment problems Customer/Vendor - Assign default cost elements

Helo Gurus,

ive tried to execute TC: F-29 Customer and F-48 Vendor down payments.

I enter all the data needed and additionaly Internal Order.

Then i get a message saying:

Maintain default revenue element in controlling area 5000

Message no. FI661

Diagnosis

CO down payment update is active in controlling area 5000. You must therefore maintain a default cost element and a default revenue element for down payments.

Procedure

Maintain the default cost elements for down payments for controlling area 5000 in the Project System implementation guide.

The maintenance is done in TC: OKEP (project system)

I created two revenue Cost elements and tried to assign them there, but it says CE are nore primary CE.

I changed it from revenue to primary, then it says that CE isnt revenue...

weird stuff

What could be the problem?

Regards

Laurynas