Unhandled Exception: System.MissingMethodException: Method not found: 'System.Threading.Tasks.Task`1<!!0> RingCentral.RestClient.Post(System.String, System.Object, System.Object)'.
at RingCentral.Subscription.Subscribe()
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start[TStateMachine](TStateMachine& stateMachine)
at RingCentral.Subscription.Subscribe()
at RingCentralPubNubDemo.Program.<>c__DisplayClass0_0.<<Main>b__0>d.MoveNext() in /Users/tyler.liu/src/dotnet/RingCentralPubNubDemo/RingCentralPubNubDemo/Program.cs:line 33
--- End of stack trace from previous location where exception was thrown ---
at RingCentralPubNubDemo.Program.Main(String[] args) in /Users/tyler.liu/src/dotnet/RingCentralPubNubDemo/RingCentralPubNubDemo/Program.cs:line 18