AEM SCREENS not able to register iPad device on AEM instance

I am not able to register an iPAD in AEM. I installed AEM screens from app store.  Please find below the details -

 iPad version - iPAD3,4 10.1.1(iOS)

firmware version - 2.2.14

webview -  cordova 4.1.1(Webkit 602.2.14) 

The status displayed is  - registration(link-up)(unauthenticated) 

I configured the screens player by going in the 'Configuration' tab in the screens player app.

But when I go to device registration tab in the screens player, the state displayed is FAILURE and the Note is - Error during registration request:

The device is not displayed in the pending devices section in the device manager

There is no connection issue as the AEM instance gets loaded on the iPAD's browser when the ip and port number of AEM instance is entered.  I was able to successfully connect an android nexus tablet to the same AEM instance.  What can be the issue for the device to not appear in the device manager? How can I debug it, any help will be really appreciated. Appreciate it. Thanks.