How do I choose which model to use in a web api post?

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ASP.NET

MVC

MVC5

EF6.0

I have a web-api, 2 tables in my SQL DB, JT and Sales. Before I add() to the database I need the poster to specify first in the uri whether he/she wants to post to JT table or Sales. My problem is that my post method only accepts one model binding, it doesn't want two like as shown on my code below. It doesn't have errors but when I post with that logic in mind it returns an error in POSTMAN that It can't bind multiple parameters ('JT' and 'Sales') to the request's content.

Here is my code:

[ResponseType(typeof(JT))]
public HttpResponseMessage PostJT(JT JT, Sales Sales, [FromUri] string tran)
        {
            try
            {
                if (ModelState.IsValid)
                {
                 if (tran == null)
                            {
                                return Request.CreateResponse(HttpStatusCode.Unauthorized, "Unauthorized Access!");
                            }
                            else
                            {
                                switch (tran)
                                {
                                    case "JT": db.JTs.Add(JT); 
                                        break;
                                    case "sales": db.Sales_.Add(Sales);
                                        break;
                                }
                            }
                            db.SaveChanges();
                            return Request.CreateErrorResponse(HttpStatusCode.OK, "Added!");
                        }
//below are just elses with return messages.