You are always welcome to join any JSTS Zwift Group Workout, and ride the course just like any other JSTS Zwift Group Ride. However, if you are interested in doing the structured workout that the rider leader designated for the meetup, then read on...
Group Workouts are not directly supported in Zwift, so there are some extra steps you must follow in order to participate in a JSTS Zwift Group Workout. Make sure that you have followed all the steps to get an invite to join a JSTS Zwift Group Workout (this includes following the leader and accepting the invite). If you are having problems joining a meetup, feel free to utilize Discord to try and get help from the other riders before the ride starts.
Don't wait until the last minute to get everything setup, as late arrivals are unable to join the meetup!