Fixed Rate billing in Customer Service

Dear All,

Am new to CS and learning, have done Fixed rate billing as follows, pls suggest me if process is wrong and any mistake and also if there is any alternative to the following.

1. Create Service Notification IW51

2. Create Service order from Service Notification only

3. Mentioned Service Product and quantity- In Operations Tab serviceable hours are updated and in components tab added component/ sparepart need for service and also updated sales area and also mentioned billing form as 01 and saved

4. Created DP80 with reference to Service Order- Price of service hours including spare part price is flowed in to DP80, saved

5. Then went to IW32 accepted Quotation system created Debit memo request for contract(but there is no contract i have created for this customer) in background and saved document.

6. VA02 feed the debit memo request doc no and entered inside, HERE Only Man hours copied to quotation not spare part which has used and quoted for service which is supposed to be copied.

Can anybody tell me where is the mistake and how to solve this issue, why spare part price not copied to debit memo request with man hours price. Also did i follow correct procedure? I mentioned billing form 01 in iw31/32 is it correct or it should be flowed from item catergory?

Regards

Murali