In order to unlock an exercise, your friend needs to tap your link, then download Seven and open it directly from the App/Google Play Store page. Then they can create a profile and complete a workout.
You can find which exercises have been unlocked by going to Seven > Settings > Invite Friends. There you will see a list of your rewarded exercises.
If you're not seeing your exercise, feel free to reach out to us at support and we'd be happy to help.