Validate App in AppStore. Non-public API usage. UDID.

I'm newbie in distributing an APP with Xamarin IOs. I'm trying to distribute my App to the AppStore and I'm getting the following error messages:

1. Apps are not permitted to access the UDID and must not use the uniqueIdentifier method of UIDevice. Please update your apps and servers to associate users with the Vendor or Advertising identifiers introduced in iOS 6.

2. Your App contains Non-Public API usage. Please review the errors, correct them, and resubmit your application.

I'm using testflight, and Oxyplot external libraries. I've found in the VerificationController.cs file that it's using the unique_identifier, as well.

Could anyone help me to solve these issues?