Click [Charge] in the sticker store and charge the amount of coins you want to exchange.
Only the in-app purchase is available for recharging the coins.
Please make your purchase after registering your payment method in the Google Play Store/App Store, and refer to the help section of each store for details.
[Google Play Store] https://support.google.com/googleplay
[App Store] https://support.apple.com/choose-country-region
However, please be aware that coins that you recharged at the respective store platforms listed above cannot be used in one another. On the other hand, items can be used on any device. (When charged on App Store, the coin only can be used on iOS devices /If charged with Google PlayStore, they can only be used on Android devices)