Hi Madhuri,
Flow goes like below
in Customer service:
SERVICE NOTIFICATION-->REPAIR ORDER ( KIND OF SALES ORDER)-->SERVICE ORDER--> ACTUAL COST --->DEBIT MEMO REQUEST -->DEBIT MEMO (BILLING)
in Project systems
SALES ORDER--->PROJECT CREATION-->ACTUAL COST-->DEBIT MEMO REQUEST-->DEBIT MEMO
in the above two cases, debit memo request is created with reference to service order or Project systems using specific transactions such as DP90 and DP91 which will populate actual or estimated cost to debit memo request to EK01 or EK02 condition types
hope it is clear
thanks
santosh