I am creating an ASP.net MVC website with a RESTful API to a SQL database. I have implemented a controller which holds the HTTP commands.

One of the commands is a POSTcommand:

     // POST: api/PoolTests
     [ResponseType(typeof(PoolTest))]
     public IHttpActionResult PostPoolTest(PoolTest poolTest)
     {
        if (!ModelState.IsValid)
        {
            return BadRequest(ModelState);
        }

        db.PoolTests.Add(poolTest);
        db.SaveChanges();

        return CreatedAtRoute("DefaultApi", new { id = poolTest.Id }, poolTest);
     }

I am using Fiddler to test out the function and I am getting some strange results. According to the automatically generated API documents the request format should be JSON with this structure (These are the fields to the connect SQL database):

               {
                 "Id": 1,
                 "SiteID": "sample string 2",
                 "Date": "sample string 3",
                 "Tub": "sample string 4",
                 "par1": 5.1,
                 "par2": 6.1,
                 "par3": 7.1,
                 "par4": 8.1
               }

In the fiddler composer I select POST and http://localhost:53660/api/PoolTests and the JSON payload {"Id": 1,"SiteID": "sample string 2", "Date": "sample string 3","Tub": "sample string 4","par1": 5.1, "par2": 6.1,"par3": 7.1,"par4": 8.1}

This results in a HTTP 400 error code.

If I send the same request with no JSON (payload) then it breaks at the line db.PoolTests.Add(poolTest); because the payload is null.

With payload if I place a break point at line if (!ModelState.IsValid) the breakpoint is never reached. It is almost like with payload the actual HTTP command is not being recognised.

Any thoughts - I appreciate that there may be some details missing.

ADDED: PoolTest Class

public class PoolTest
{
    public int Id { get; set; }
    public string SiteID { get; set; }
    public string Date { get; set; }
    public string Tub { get; set; }
    public double par1 { get; set; }
    public double par2 { get; set; }
    public double par3 { get; set; }
    public double par4 { get; set; }
}

FIDDLER Screenshot Added:

I have added the content-type and now I hit the breakpoint, but the Pooltest is reported as being null