Back in time whatsapp was not free for some countries and for some countries a 1$ subscription fee was required. But since facebook brought whatsapp with 19 $Billion, they made it completely free. But how they are making money.
Do you know what is the most valuable things in the world, it's information. When facebook brought whatsapp, it has one billion users. That means facebook paid 19$ per user. But after buying whatsapp their revenue increased dramatically from add service.
In short facebook got huge amount of data from whatsapp which are using to show interest based add on facebook. Suppose that you have send a message about a book via whatsapp. Now if you log into your facebook, you will see an add related to book. This the way facebook using whatsapp data.
Rumors around that facebook knows everything about you. They use your data for advertisement also they sell data to other broker. Hope that this is just a rumor.
Goodbye today. Best of luck for my blog readers.