Hello G Dharani Kumar,
Instead of using a message definition I would advise you in this case to first create a JSON Structure:
Copy paste your snippet in there click on format then click on refresh and then OK
Then create a import mapping based on this Structure/
Select JSON Structure and click select all and save:*
This will be the structure you need, to make life even easier select automatic mapping then mendix create the structure NP in your domain model;
Now you can make it again if you want as a message definition and you can map your full json.
*
Hope this helps
Good luck!