MonoTouch does not support dynamic proxy code generation.

[musab-alrmmah]

{System.InvalidOperationException: MonoTouch does not support dynamic proxy code generation. Override this method or its caller to return specific client proxy instance

  at System.ServiceModel.ChannelFactory`1[TChannel].CreateChannel (System.ServiceModel.EndpointAddress address, System.Uri via) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.0.0.15/src/Xamarin.iOS/mcs/class/System.ServiceModel/System.ServiceModel/ChannelFactory_1.cs:141 
  at System.ServiceModel.ChannelFactory`1[TChannel].CreateChannel (System.ServiceModel.EndpointAddress address) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.0.0.15/src/Xamarin.iOS/mcs/class/System.ServiceModel/System.ServiceModel/ChannelFactory_1.cs:115 
  at System.ServiceModel.ChannelFactory`1[TChannel].CreateChannel () [0x00006] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.0.0.15/src/Xamarin.iOS/mcs/class/System.ServiceModel/System.ServiceModel/ChannelFactory_1.cs:110 
  at System.ServiceModel.ClientBase`1[TChannel].CreateChannel () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.0.0.15/src/Xamarin.iOS/mcs/class/System.ServiceModel/System.ServiceModel/ClientBase.cs:266 
  at System.ServiceModel.ClientBase`1[TChannel].get_InnerChannel () [0x00008] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.0.0.15/src/Xamarin.iOS/mcs/class/System.ServiceModel/System.ServiceModel/ClientBase.cs:186 
  at System.ServiceModel.ClientBase`1[TChannel].get_Channel () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.0.0.15/src/Xamarin.iOS/mcs/class/System.ServiceModel/System.ServiceModel/ClientBase.cs:192 

[StephenBonikowsky]

@musab-alrmmah Unfortunately there are a number of compatibility issues right now between Xamarin's Mono and WcfCore. Here is a link to a few issues:
https://github.com/dotnet/wcf/issues?q=is%3Aopen+is%3Aissue+label%3AXamarin

In your case the simple explanation is that WcfCore uses 'dynamic proxy' and Xamarin implemented a different solution. Sounds like you have a NetStandard app using WcfCore code running on Xamarin.

Adding @marek-safar and @akoeplinger from Xamarin team.