missing activity APPROVE_WAIT_FOR_H

Process "xxxxx_Order_line bill only" is missing activity APPROVE_WAIT_FOR_H   which is defined as the waiting/continuation of activity   APPROVE_CONT_L in process "yyyy_Order_HEADER With Approval"

Above Message is Standard and provided by Oracle to validate the workflow.

Please note that this is not an error , it is actually result of validation built in Oracle Order Management Transaction Type User Interface (UI).This type of error generally popup when you are trying to assign wrong line workflow with the Order Header workflow.
In this particular Error case user is trying to associated line workflow Process
"xxxxx_Order_line Bill Only " with the Order header workflow ""yyyy_Order_HEADER With Approval"".From name of header workflow it is very clear that header workflow is has activity related to approval.Please note that Order Header workflow that required Approvals , always has  activity "APPROVAL_CONT_L" , this is a seeded activity and .
In the  "Node Attributes" tab of this activity we can see 2 properties

1. Waiting Activity  - APPROVE_WAIT_FOR_H
2. Waiting flow  - Details

These 2 attributes clearly indicates that if we have ""APPROVAL_CONT_L" activity in Header then the Line(Details) should have an activity "APPROVE_WAIT_FOR_H".

And if we don't have "APPROVE_WAIT_FOR_H" in the Order line then when ever you assign the line workflow with missing Approval activity to a header that has approval activity and hit the "Validate" buttin system will throw this error.
Note - This is very common when customer customized the workflow and assign wrong line workflow with the header workflow.

thanks