Android and SSL Certificate

Question

Hi,
I'm using Xamarin Forms and I want to access XML file from Android app to check for existing updates, I was using Plesk hosting but now Let's Encrypt SSL does not support Android operating systems before 7.1.1.
App crashes here:

            XmlDocument doc = new XmlDocument();
            doc.Load("https://mysite.com/xml/update.xml");
            XmlNode node = doc.DocumentElement.SelectSingleNode("/App/myapp");
            int lastVertion = int.Parse(node.InnerText.ToString());

How do I solve this issue?

Thanks