Hey @Tufted Donkey!
Just to make things clear, Nightbot only syncs Twitch moderators, Nightbot regulars, and I believe Twitch VIPs as well (not 100% sure about that one, but quite confident); it doesn't sync Twitch subscribers, for that Discord has its own integration.
Since Nightbot already syncs some users' roles I won't ask you to check your Discord server roles' settings, they're likely good, unless there's a specific category of users it doesn't sync. For future readers, if it doesn't sync anyone, or if it doesn't sync a specific category of users, make sure Nightbot's role is above the roles it has to assign, and that it has the permission to Manage Roles.
However, for Nightbot to give users their roles, they must have their Twitch account linked to their Discord account, and they must send at least one message in a channel in which Nightbot can read messages (check your channels' permissions). The sync should happen within 15 minutes.