ServicePointManager.ClientCipherSuitesCallback has been marked as Obsolete in Mono, and Android builds of ModernHttpClient no longer compile. https://github.com/mono/mono/blob/86b5cde6c07809d81b592973f002ecf16cc22bf6/mcs/class/System/System.Net/ServicePointManager.extra.cs#L22-L23 This change is already in the current stable release of Xamarin.Android (6.1.0.71)