Groupon didn't get your email from Facebook, but we need it to sign you up.
If you'd like to share it with us so you can take advantage of Facebook Login, you can update your Facebook permissions to give us access to your email. If not, you can always sign up for a Groupon account without using Facebook.
My daughter is a dancer and her knees were starting to get sore from dancing 2 hours a day. I bought these in a size small for her (she's 11 and very thin) and they fit perfect. Follow the sizing for the correct fit. They provide support without restricting her movement and her knees are much less sore now.