post data to sqlserver using MVC web api

I am trying to register using mvc web api in a simple way:

This is my users model:

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web

Namespace WebApi.Models
    Public Class users
        Public Property userid() As Guid
        Public Property logintype() As String
        Public Property username() As String
        Public Property password() As String
        Public Property email() As String
        Public Property createddate() As DateTime

    End Class
End Namespace

This is my userdetails model:

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Data
Imports System.Data.SqlClient

Namespace WebApi.Models
    Public Class userdetails
        Private users As New List(Of users)()
        Private con As SqlConnection
        Private da As SqlDataAdapter
        Private ds As New DataSet()
        Dim userid As String = System.Guid.NewGuid.ToString()
        Public Function RegisterUser(ByVal username As String, ByVal password As String, ByVal email As String, ByVal logintype As String) As String
            'Create ConnectionString and Inser Statement
            Try
                Using cn As New SqlConnection("Data Source=.\sqlexpress;Initial Catalog=usersList;Persist Security Info=True;User ID=sa;Password=*****")
                    cn.Open()
                    Dim cmd As New SqlCommand()
                    cmd.CommandText = "INSERT INTO users (userid,logintype,username, password, email, createddate) VALUES(@userid,@logintype,@username,@password,@email,@createddate)"

                    Dim strDate As String = Date.Now.ToString("MM/dd/yyyy hh:mm:ss tt")

                    Dim param1 As New SqlParameter()
                    param1.ParameterName = "@userid"
                    param1.Value = userid
                    cmd.Parameters.Add(param1)

                    Dim param2 As New SqlParameter()
                    param2.ParameterName = "@logintype"
                    param2.Value = logintype
                    cmd.Parameters.Add(param2)

                    Dim param3 As New SqlParameter()
                    param3.ParameterName = "@username"
                    param3.Value = username
                    cmd.Parameters.Add(param3)

                    Dim param4 As New SqlParameter()
                    param4.ParameterName = "@password"
                    param4.Value = password
                    cmd.Parameters.Add(param4)

                    Dim param5 As New SqlParameter()
                    param5.ParameterName = "@email"
                    param5.Value = email
                    cmd.Parameters.Add(param5)

                    Dim param6 As New SqlParameter()
                    param6.ParameterName = "@createddate"
                    param6.Value = strDate
                    cmd.Parameters.Add(param6)

                    cmd.Connection = cn
                    cmd.ExecuteNonQuery()
                    cn.Close()
                End Using
                Return True
            Catch
                Return False
            End Try
        End Function
        Public Function GetAll() As IEnumerable(Of users)
            con = New SqlConnection("Data Source=.\sqlexpress;Initial Catalog=usersList;Persist Security Info=True;User ID=sa;Password=*****")
            da = New SqlDataAdapter("select * from users", con)
            da.Fill(ds)
            For Each dr As DataRow In ds.Tables(0).Rows
                users.Add(New users() With {.userid = Guid.Parse(dr(0).ToString()), .logintype = dr(1).ToString(), .username = dr(2).ToString(), .password = dr(3).ToString(), .email = dr(4).ToString(), .createddate = DateTime.Parse(dr(5).ToString())})
            Next dr
            Return users
        End Function

        Public Function GetUserById(ByVal userid As String) As String

            Dim con As New SqlConnection("Data Source=.\sqlexpress;Initial Catalog=usersList;Persist Security Info=True;User ID=sa;Password=*****")
            con.Open()
            Dim email As String = String.Empty
            Dim cmd As New SqlCommand("select * from users where userid=@userid", con)
            cmd.Parameters.AddWithValue("@userid", userid)
            Using sdr As SqlDataReader = cmd.ExecuteReader()
                If sdr.Read() Then
                    email = sdr("email").ToString()
                End If
            End Using
            con.Close()
            Return email
        End Function
    End Class
End Namespace

This is my userdetails controller:

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Net
Imports System.Net.Http
Imports System.Web.Http
Imports MvcApplication1.WebApi.Models

Namespace WebApi.Controllers
    Public Class usercontroller
        Inherits ApiController
        Private Shared ReadOnly repository As New userdetails()
        Public Function RegisterUser(<FromBody()> ByVal username As String, <FromBody()> ByVal password As String, <FromBody()> ByVal email As String, <FromBody()> ByVal logintype As String) As String
            Return repository.RegisterUser(username, password, email, logintype)
        End Function
        Public Function GetAllUsers() As IEnumerable(Of users)
            Return repository.GetAll()
        End Function
        Public Function GetEmail(ByVal id As String) As String
            Return repository.GetUserById(id)
        End Function
    End Class
End Namespace

Now I'm able to get the userdetails with Id but when trying to post the details its not hitting the breakpoint and this is how I'm trying to post using fiddler and getting 500 response:

Can anyone say me how do I post the data in a correct way?