Arcane Online is free to play, however you may want to purchase some Rubies in the in-app premium shop to help you in your progress.
In order to avoid accidental in-app purchases in Arcane Online, you will need to adjust your Google Pay Store settings.
You can follow the 4 steps below:
1. Access the Google Play Store
2. Enter the "Settings" menu.
3. Go to "User Controls" and activate "Use password to restrict purchases".
4. Enter and confirm your password to change this setting.
Now any in-app purchase will require you to enter you security password.
Warning: once you have entered your password and confirmed a purchase, you can make more purchases for 30 minutes without having to enter your password again!