The mobile payments app Paytm and the messaging app WhatsApp are stepping up their rivalry in India. WhatsApp is due to launch a payments service in India in the next few months. In a pre-emptive strike in response, Paytm has just launched a messaging service within its app. The service, called Inbox, is fully integrated into the Paytm app and has chat features including photo and video sharing. Paytm has 100 million monthly users in India, compared to WhatsApp's 200 million.