Viber is a free communication app especially when one user chats or call to other Viber users. Since there are certain ways the company is making money . The first thing from where the app developer earns is from Viber stickers. Some are free while others need to be purchased before using.
Secondly, for playing Viber games, you have to pay a fee to proceed to advance levels. Some games are free to play while others need a subscription for activation. The last but not least source through which Viber is making money is the Viber Out feature.
People pay a fee to make a call to a landline or other cell number having no Viber app. The charges vary from country to country. You have to pay an extra fee for an international call. By this means the app is making a lot of money and earning revenues.