diff --git a/Example/Example/SearchResultsCollectionViewController.swift b/Example/Example/SearchResultsCollectionViewController.swift
index 70e765a..de628a1 100644
--- a/Example/Example/SearchResultsCollectionViewController.swift
+++ b/Example/Example/SearchResultsCollectionViewController.swift
@@ -84,7 +84,7 @@ class SearchResultsCollectionViewController: UICollectionViewController {
         
         // call tracking api here to register the click
         // alternately, you can present similar images or recommend them to users in the image detail page
-        let params = ViTrackParams(accessKey: ViSearch.sharedInstance.client!.accessKey, reqId: self.reqId, action: "click")
+        let params = ViTrackParams(reqId: self.reqId, action: "click")
         params?.imName = im_name
         
         ViSearch.sharedInstance.track(params: params!) { (success, error) in
diff --git a/README.md b/README.md
index 3632c44..3591ecc 100644
--- a/README.md
+++ b/README.md
@@ -549,7 +549,7 @@ User action (e.g. click on an image after search) can be sent in this way:
 
 ```swift
 
-let params = ViTrackParams(accessKey: ViSearch.sharedInstance.client!.accessKey, reqId: recentReqId, action: "click" )
+let params = ViTrackParams(reqId: recentReqId, action: "click" )
                                     
 // You can also append an im_name field
 params.imName = "example_clicked_im_name"
diff --git a/ViSearchSDK/ViSearchSDK/Classes/Request/ViTrackParams.swift b/ViSearchSDK/ViSearchSDK/Classes/Request/ViTrackParams.swift
index 81498dc..a3f8139 100644
--- a/ViSearchSDK/ViSearchSDK/Classes/Request/ViTrackParams.swift
+++ b/ViSearchSDK/ViSearchSDK/Classes/Request/ViTrackParams.swift
@@ -8,16 +8,14 @@ public class ViTrackParams : ViSearchParamsProtocol{
     public var imName : String?
     public var reqId  : String
     public var cuid   : String?
-    var cid    : String
-    
-    //MARK: init
+    var cid    : String?
     
     /// Init tracking parameters. For example, after user search for images, we want to track which image they clicked
     ///
     /// - parameter accessKey: API access key
     /// - parameter reqId: recent request id e.g. search for similar images
     /// - parameter action: tracking action e.g. click, add to cart, etc. Currently only click is supported
-    public init?(accessKey: String, reqId : String , action: String ) {
+    public convenience init?(accessKey: String, reqId : String , action: String ) {
         
         if accessKey.isEmpty {
             print("\(type(of: self)).\(#function)[line:\(#line)] - error: accessKey parameter is missing")
@@ -25,23 +23,30 @@ public class ViTrackParams : ViSearchParamsProtocol{
             return nil
         }
         
+        self.init(reqId: reqId, action: action)
+        
+        self.cid = accessKey
+        self.cuid = nil
+        self.imName = nil
+    }
+    
+    /// Init tracking parameters. For example, after user search for images, we want to track which image they clicked
+    /// Assumption: access key will be passed by client later
+    /// - parameter reqId: recent request id e.g. search for similar images
+    /// - parameter action: tracking action e.g. click, add to cart, etc. Currently only click is supported
+    public init?(reqId : String , action: String){
         if reqId.isEmpty {
             print("\(type(of: self)).\(#function)[line:\(#line)] - error: reqId parameter is missing")
-            
             return nil
         }
         
         if action.isEmpty {
             print("\(type(of: self)).\(#function)[line:\(#line)] - error: action parameter is missing")
-            
             return nil
         }
-        
-        self.cid = accessKey
+
         self.reqId = reqId
         self.action = action
-        self.cuid = nil
-        self.imName = nil
     }
     
     //MARK: search protocol
diff --git a/ViSearchSDK/ViSearchSDK/Classes/ViSearch.swift b/ViSearchSDK/ViSearchSDK/Classes/ViSearch.swift
index 8fb9630..c480205 100644
--- a/ViSearchSDK/ViSearchSDK/Classes/ViSearch.swift
+++ b/ViSearchSDK/ViSearchSDK/Classes/ViSearch.swift
@@ -92,7 +92,7 @@ open class ViSearch: NSObject {
         return nil
     }
     
-    // track the API calls and various actions
+    /// track the API calls and various actions
     /// Tracking API
     @discardableResult public func track(params: ViTrackParams,
                                          handler:  ( (_ success: Bool, Error?) -> Void )?
diff --git a/ViSearchSDK/ViSearchSDK/Classes/ViSearchClient.swift b/ViSearchSDK/ViSearchSDK/Classes/ViSearchClient.swift
index 0a68826..2bbfbb2 100644
--- a/ViSearchSDK/ViSearchSDK/Classes/ViSearchClient.swift
+++ b/ViSearchSDK/ViSearchSDK/Classes/ViSearchClient.swift
@@ -149,6 +149,8 @@ open class ViSearchClient: NSObject, URLSessionDelegate {
                       handler:  ( (_ success: Bool, Error?) -> Void )?
                       ) -> Void {
         
+        params.cid = accessKey
+        
         // different url for tracking
         let url = requestSerialization.generateRequestUrl(baseUrl: trackUrl , apiEndPoint: .TRACK , searchParams: params)
         let request = NSMutableURLRequest(url: URL(string: url)! , cachePolicy: .useProtocolCachePolicy , timeoutInterval: timeoutInterval)