The images indicate that the WhatsApp payment method will utilize the Unified Payments Interface (UPI), an instant real-time payment system developed by National Payments Corporation of India that facilitates inter-bank transactions.
UPI is regulated by the Reserve Bank of India and works by instantly transferring funds between two bank accounts on a mobile platform. The same system is also used by Swedish-based phone number lookup service Trucaller, which introduced user-to-user payments in India via a tie-in with ICICI Bank last April.
WhatsApp's UPI setup process appears to involve just a couple of steps, after which users can presumably instantly transfer cash to other WhatsApp users' bank accounts. The payment system could be ready for launch in India in the first quarter of 2018, although WhatsApp's plans for a similar payments system for users in other countries remain unclear.
Facebook has had a payments system in its Messenger app for some time in the U.S., but WhatsApp remains far more popular in India and is heavily used there as an e-commerce portal, despite not yet offering any features that specifically support the practice.