Between's 'Hearts' are required to purchase stickers or paid products.
Go to the More tab and press the 'Purchase Hearts' button to charge your Hearts first, and then pick out a product you want to buy.
1. Purchased Hearts, and products purchased with Hearts cannot be refunded regardless of whether or not you used them.
2. You can't transfer Hearts between Android and iOS devices. Please only use your Hearts with the device you purchased them with (e.g. Hearts purchased using an Android device can't be transferred to an iPhone).
3. You can't gift purchased Hearts to your partner.