NEW DELHI, Nov 26 (Reuters) - WhatsApp (FB.O) has won regulatory approval to double the number of users on its payments service in India to 40 million, a source with direct knowledge told Reuters on Friday. The company had requested that there should be no cap on users of its payment service in India. Instead, the National Payments Corporation of India (NPCI)this week told the company it could double the user base to which it can offer its payment service - currently restricted to 20 million - the source said. WhatsApp is owned by Facebook, which recently changed its name to Meta. The source said the new cap would still hinder the company"s growth prospects given that WhatsApp"s messenger service has more than 500 million users in India, the company"s biggest market. It was not clear when the new cap would come into effect. WhatsApp did not immediately respond to a request for comment, while the NPCI declined to comment. WhatsApp competes with Alphabet Inc’s (GOOGL.O) Google Pay, SoftBank- and Ant Group-backed Paytm (PAYT.NS) and Walmart’s (WMT.N) PhonePe in India"s crowded digital market. The NPCI gave WhatsApp approval to start its payments service last year after the company spent years trying to comply with Indian regulations, including data storage norms that require all payments-related data to be stored locally. WhatsApp has almost reached its user base of 20 million for payment services, said the source, who declined to be identified as the details are private. Online transactions, lending and e-wallet services have been growing rapidly in India, led by a government push to make the country’s cash-loving merchants and consumers adopt digital payments.