Hi Nikhil ,
Try creating a new doc flow for the transaction you are trying to add doc_flow to using CRMD_order transaction. Put a break point in CRM_ORDER_MAINTAIN. Supply the same parameters in your case. Then it would work.
Better if possible try changing the doc_flow from CRMD_ORDER and then put a break point CRM_ORDER_MAINTAIN.
You might be missing a small parameter value here or there. With this approach you can find out which one.
Regards,
Kavindra