You will need to use Coins to purchase stickers in the LINE app. If you don't have enough Coins, you'll need to purchase some before you can buy stickers.
If you have enough Coins, try purchasing stickers with the following steps:
1. Go to More > Sticker Shop.
2. Select the sticker set you want to buy.
3. Tap Purchase.
Tap here to open the Sticker Shop page from your smartphone.