Creating a calculation logic as a REST API for Postman Request consists of these steps: 

...

{
    "data": {
        "CustomerID": "111980",
        "ProductID": "1504795"
    }
}

Now create execute a calculation logic which returns the some expected data and make it receive the request parameter, e.g ProductID, using api.input("ProductID").

Request Logic with POSTMAN

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