have tried formatting it in a ton of different ways but it keeps saying, "Discord has returned error Code - 0: 404: Not Found", any help would be appreciated. 

message.CreateReaction(Client, "800214781554065471"); have tried ID and name but it still can't find the emoji

Solved through discord but adding here in case other people need help.

private void DoTest2()
{
    byte[] encodedEmoji = Encoding.UTF8.GetBytes("😀");
    string hexString = HttpUtility.UrlEncode(encodedEmoji);
    
    Channel.GetChannel(_client, ChannelId, channel =>
    {
        channel.CreateMessage(_client, "This is a message", message =>
        {
            //Custom Emoji Reaction
            message.CreateReaction(_client, "mjtest:800428531015483412");
            
            timer.In(5f, () =>
            {
                //Built In Emoji Reaction
                message.CreateReaction(_client, hexString);
            });
        });
    });
}​