How to pass a JNI C# class into Java?

I'm trying to call a Java method from C#, it's called like this from java:

 EgamePay.pay(thisActivity, payAlias, new EgamePayListener() {
             @Override
             public void paySuccess(String alias) {
             }

             @Override
             public void payFailed(String alias, int errorInt) {
             }

             @Override
             public void payCancel(String alias) {
             }
         });

The first two parameters are ok, but how do I pass the EgamePayListner through in C#? Simply creating a C# class with the same functions won't work...

Here's what I'm doing currently:

 using (AndroidJavaClass jc = new AndroidJavaClass("cn.egame.terminal.smspay.EgamePay"))
         {
             System.IntPtr cls_Activity = AndroidJNI.FindClass("com/unity3d/player/UnityPlayer");
             System.IntPtr fid_Activity = AndroidJNI.GetStaticFieldID(cls_Activity, "currentActivity", "Landroid/app/Activity;");
             object[] p = { fid_Activity, "payAlias", new EgamePayListener() };
             jc.CallStatic("pay", p);
         }
 
 ..
 
  class EgamePayListener
     {
         public void paySucess(string alias)
         {
         }
 
         public void payFailed(string alians, int errorInt)
         {
         }
 
         public void payCancel(string alias)
         {
         }
     }