How do I write a post method that accepts JSON in Nancy, and how do I call it from a C# client?

I wrote the following module in Nancy

    public class CategoryModule : NancyModule
{
    public CategoryModule()
    {
        //At this moment just Show Hello world
        Get["/"] = _ => { return "Nancy says hello!"; };
        //Get["/"] = parameters => "Hello World!";
        GetCategories();
        SetCategory();
    }


     void GetCategories()
    {
        Get["/Catergories"] = _ =>
        {

            var catergoryRepository = new CategoryRepository();
            var categorycollection = catergoryRepository.GetCategoryInfo();
            return Negotiate.WithStatusCode(HttpStatusCode.OK).WithModel(categorycollection.ToArray());
        };
    }

     void SetCategory()
     {
         Post["/Catergories/{categryName:string}"] = _ =>
         {
             var catergoryModel = this.Bind<Category>();
             catergoryModel.PK_CategoryId = Guid.NewGuid();
             catergoryModel.CategoryName = _;
             return HttpStatusCode.OK;
         };
     }
}

I am using chrome POSTMAN to test the module. If I call http://192.168.1.4:8888/Categories in POSTMAN, I can get breakpoints in "GetCategories()" . But if I call http://192.168.1.4:8888/Catergories/categryName=test, I ca n't get the breakpoint in SetCategory() . I'm new to Nancy and not sure if my method of posting is correct.

anyone can provide

1. Example of Post method accepting Jason as parameter
2. Example of calling it from client

I couldn't find the simple example above in their documentation.

Notice

I'm hosting Nancy's self-hosted environment with the following code

var server = new Nancy.Hosting.Self.NancyHost(new Uri("http://192.168.1.4:8888"));

Below is the category model

    public class Category
{
    public Guid PK_CategoryId { get; set; }
    public string CategoryName { get; set; }

}