In-app purchases facility means you can purchase any goods or services from the application running on you mobile phone.
The process to in-app purchases through Google Play from Viber is very simple. First of all, you have to tap on the "Play Store" app in your mobile to open it.
When the play store is open then click on the three lines in the upper-left corner of the screen. The different options open on screen. Tap on "Settings" from these options.
Then click on "Require authentication for purchases". Further tap on "For all purchases through Google Play on this device" tab.
Now it requires your account password. Type your password and then click "OK" button to confirm. The process is complete. Now, you can make in-app purchases.
