When sitting at a blackjack table and not participating in a game you get a NRE error:

Failed to call hook 'OnPlayerChat' on plugin 'BetterChat v5.2.12' (InvalidOperationException: Chat channel is set to Cards, however the player is not in a participating in a card game.)
	at Oxide.Plugins.BetterChat.SendBetterChatMessage (Oxide.Plugins.BetterChat+BetterChatMessage chatMessage, ConVar.Chat+ChatChannel chatchannel) [0x0020e] in <5114c84c1ae04466b358c94299f44af5>:0
	at Oxide.Plugins.BetterChat.OnPlayerChat (BasePlayer bplayer, System.String message, ConVar.Chat+ChatChannel chatchannel) [0x00049] in <5114c84c1ae04466b358c94299f44af5>:0
	at Oxide.Plugins.BetterChat.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x000ed] in <5114c84c1ae04466b358c94299f44af5>:0
	at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <09575a60985045248bcb43b20faeeb99>:0
	at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <bae5f1223fce49c493b01571c99dce02>:0
	at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <bae5f1223fce49c493b01571c99dce02>:0

When you first sit at a table, you have to add your scrap and then hit "play". Prior to hitting play, you can participate in the card chat while not being in a game.