WebAPI Multiple Put/Post parameters

[HttpPost]
public string MyMethod([FromBody]JObject data)
{
    Customer customer = data["customerData"].ToObject<Customer>();
    Product product = data["productData"].ToObject<Product>();
    Employee employee = data["employeeData"].ToObject<Employee>();
    //... other class....
}

using referance

using Newtonsoft.Json.Linq;

Use Request for JQuery Ajax

var customer = {
    "Name": "jhon",
    "Id": 1,
};
var product = {
    "Name": "table",
    "CategoryId": 5,
    "Count": 100
};
var employee = {
    "Name": "Fatih",
    "Id": 4,
};

var myData = {};
myData.customerData = customer;
myData.productData = product;
myData.employeeData = employee;

$.ajax({
    type: 'POST',
    async: true,
    dataType: "json",
    url: "Your Url",
    data: myData,
    success: function (data) {
        console.log("Response Data ↓");
        console.log(data);
    },
    error: function (err) {
        console.log(err);
    }
});