internal static void RaiseOnSuccess(PurchaseDetails purchaseDetails)
 {
     if (OnSuccess != null)
     {
         OnSuccess (purchaseDetails);
     }
 }
 internal static void RaiseOnRestore(PurchaseDetails purchaseDetails)
 {
     if (OnRestore != null)
     {
         OnRestore (purchaseDetails);
     }
 }