Objective-C native plugin implementation not working

I am trying to add a plugin i have created in Objective-C to unity. At this point my plugin is very simple. It is one of the examples in the unity manual "float FooPluginFunction () { return 5.0F; }" My plugin is written in Objective-C and is below.

 WindowsController.h
 #import "Foundation/Foundation.h"
 #import "Cocoa/Cocoa.h"
 
 @interface MYSDK : NSObject
 
 
 @end 
 
 //#ifdef __cplusplus
 //extern "C" float MySDKFooBarCFunction(){
 //#endif
 //
 //#ifdef __cplusplus
 //}
 //#endif

The commented out section in code above is other method that i have tried.

 WindowsController.m
 #import "WindowController.h"
 
 @implementation MYSDK
 
 - (float)myNumber{
     return 5.0f;
 }
 
 @end
 
 #ifdef __cplusplus
 extern "C" float MySDKFooBarCFunction{
     return myNumber();
 }
 #endif

My Unity Script is written in c# and is below.

 PlayThatButton.cs
 using System.Runtime.InteropServices;
 using UnityEngine;
 
 
 public class PlayThatButton : MonoBehaviour{
 
 #if UNITY_IPHONE && !UNITY_EDITOR
    
        // On iOS plugins are statically linked into
        // the executable, so we have to use __Internal as the
        // library name.
        [DllImport ("__Internal")]
 
 #else
 
     // Other platforms load plugins dynamically, so pass the name
     // of the plugin's dynamic library.
     [DllImport ("unity_playbutton_test")]
 
 #endif
 
     private static extern float MySDKFooBarCFunction ();
 
 
 
     private void Awake(){
         print(MySDKFooBarCFunction());
     }
 }
 

These images are here to show how i have structured everything in unity. I have added the PlayThatButton.cs file to the Main Camera object. The error i am receiving from Unity is "EntryPointNotFoundException: MySDKFooBarCFunction PlayThatButton.Awake () (at Assets/Scripts/PlayThatButton.cs:27)"

I have searched the internet finding many possible solutions, but none have worked. Clearly i am doing something wrong or forgot to implement something in addition to what i have. I am at a loss of where to go next. Any help in solving this issue would be much appreciated. Let me know if i have not included anything in the descriptions above to help you help me.

Thank you,