Cannot assign data to Request body

My question:
I cannot assign data from json file to the Request body when run collection with Json file or CSV, currently result of the request body is “null”. Please help me with this issue, thanks

Here is my script :
pm.test(“Check Reponse Mess”, function (){
console.log(pm.iterationData.get(“Messagerequest”));
});

Details (like screenshots):
Run Collection
image

My body:
image

Json file:
image
image