Can't show CustomRelativeLayout on Xamarin.Android

I’m trying to use PDFTron for Xamarin Android. I want to render and paint my custom annotations, without using their annotation system. According to their documentation in https://www.pdftron.com/documentation/xamarin/guides/ui-customization/custom-view/android/ You can add a CustomRelativeLayout which doesn’t work. It basically renders nothing in top of the PDF

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I hosted the whole solution in here http://s000.tinyupload.com/index.php?file_id=14574507524295393508 so it’s easy to test and see if someone can see what’s wrong.

Thanks!