DiscordClient.GetChannelAsync

Hello, I put on my discord the channel id but its not working here is my code

var a = Client.GetChannelAsync(ChannelID).GetAwaiter().GetResult();
var myMsg = a.GetMessagesAsync(1).GetAwaiter().GetResult();

var a = Client.GetChannelAsync(ChannelID).GetAwaiter().GetResult();
var myMsg = a.GetMessagesAsync(1).GetAwaiter().GetResult();

DiscordClient.GetChannelAsync - C#