@Sakana
The "subscribed to" is probably meant for if they host a channel so it won't trigger it.
@Khonor
That said, it's probably best to enclose that halt in brackets and change it to an OR operator on top of $nick != twitchnotify.
if ($nick != twitchnotify) || ($istok($1-,subscribed to,32)) { halt }
That should make it where if someone tries to trigger it without being "twitchnotify" and if you're hosting a channel it won't trigger the command.