Revenue recognition for customer contracts

Dear experts,

I currently have the requirement from our customer to accrue revenue as well as costs for fixed price customer contracts.
Meaning our customer is selling services on fixed price bases over customer contracts but is on the other side purchasing
the sold services as well.

Therefore the revenue as well as costs (booked on the contract positions via supplier invoices) should be accrued.

I've already tested the accrual method "Straight line - even periods" which works perfectly fine and as requested from our

customer for the revenue. But it seems that the costs do not get accrued.

Is there a way to accure and recognize the costs booked to the contract position in the same way as the accrual method
"Straight line -even periods" does it for the revenue?

Many thanks in advance

Cheers Horst Lambauer