Instagram/Kayla ItsinesKayla Itsines is a social media and fitness star. The 24-year-old Australian behind the Bikini Body Guide has legions of fans and over four million followers on Instagram. But now, People is reporting that her fans are furious because her app, Sweat With Kayla, is charging them unexpectedly and that the subscription fee is nearly impossible to get out of. People claims that clients are downloading her app for a free 7-day trial, but that they have to enter their credit card info first.