New to Scripting. How to handle dynamic values in Loadrunner scripting for contents in the body from a web custom request function

In the below custom request, the body contents like "trailerId\"\"TRL0000284\",\"masterReceiptId\" keeps changing for every new requests. I couldnt find the response of the contents in the snapshot view to correlate. Please help. New to Scripting.

web_custom_request("assign",     
    "URL=https://,     
    "Method=PUT",     
    "TargetFrame=",     
    "Resource=0",     
    "Snapshot=t1.inf",     
    "Mode=HTML",     
    "Body={\"trailerNumber\":\{pTrailerNo}\",\"trailerId\":\"TRL0000284\",\"masterReceiptId\":\"1010899\",\"warehouseId\":\"3348\"}",