URGENT Facebook GameRequestDialog not calling callbacks

I'm using the Xamarin.Facebook.Android package for this. The dialog displays correctly and the requests go through to the correct recipients but the callbacks never get called. I'm not 100% sure where I'm supposed to get the CallbackManager from.

I've been stuck on this issue for about a week now. It's holding up a release of our app.

I'd greatly appreciate any help.

`
public class FacebookService : IFacebookService
{
public void InviteFriends(FacebookInviteCallbacks facebookInviteCallbacks)
{
if (AppInviteDialog.CanShow())
{
var activity = Xamarin.Forms.Forms.Context as Activity;
var content = new GameRequestContent.Builder().
SetTitle("Check out this game").
SetMessage("Check out this game I play!").
Build() as GameRequestContent;

        var dialog = new GameRequestDialog(activity);

        dialog.RegisterCallback(CallbackManagerFactory.Create(), new MyFacebookCallback(facebookInviteCallbacks));
        dialog.Show(content);                

    }
}       

}

public class MyFacebookCallback : Java.Lang.Object, IFacebookCallback
{
private FacebookInviteCallbacks facebookInviteCallbacks;

public ImcFacebookCallback(FacebookInviteCallbacks facebookInviteCallbacks)
{
    this.facebookInviteCallbacks = facebookInviteCallbacks;
}

public void OnCancel()
{
    System.Diagnostics.Debug.WriteLine("Cancelled sending invite");
}

public void OnError(FacebookException error)
{
    facebookInviteCallbacks.FailedCallback(error.Message);
}

public void OnSuccess(Java.Lang.Object result)
{
    System.Diagnostics.Debug.WriteLine(result);
}

}`