If you are using a new device, you can simply restore your purchase on your new device. You do not need to purchase it again.
For Android users, make sure that you are logged in to the same Google Play account you had on the old device. From the Play Store, go to Menu and select Subscriptions. Select QuizClash and then tap Restore.
For iOS users, make sure that the device has the same Apple ID you had on the previous device. Go to Account Settings and select QuizClash. Scroll down to the bottom, tap Restore Purchases and choose QuizClash. This will restore your purchase. In some cases, you may need to log out of your Apple ID, then log back in, then restart the device, in order for your purchase to be restored.