Three usual reasons.
You're not on a roster yet. The app says so and offers Join a club. Enter your club's join code.
Your coach hasn't put you in a squad. You've joined, but you can't be scheduled until they give you a squad and grade in the web app. Ask them; it takes a moment.
There are no sessions yet. Sessions come from the club's training days. If the club hasn't set them up, there's nothing to show.