Pretty sure twitchclient 3 is deprecated and no longer used at all.
Also, make sure you wait for your OP status to be identified by mIRC. You may want to switch it to check for isop in $msgtags.
(user-type=mod isin $msgtags)
and request the following capabilities.
raw CAP REQ :twitch.tv/membership
raw CAP REQ :twitch.tv/tags
raw CAP REQ :twitch.tv/commands