Hello Nandish,
Just to remind you that you need to fire your GET operation by passing the navigation property defined between your Header and Item entities.
The response of this should be used as the payload.
When you do this way you will not get these kind of errors.
So please check.
Property names are Case Sensitive.
You need to make sure that you pass same Property Names which are mentioned in your Gateway Model.
Please check the property names and pass them in payload accordingly.
Its easy to build your payload manually as well XML or JSON ->
See below how you can build manually :
Step by Step development for CREATE_DEEP_ENTITY operation
You can also build JSON payload for the above XML format as well.
Regards,
Ashwin
