WhatsApp will roll out its payments service in India, its biggest market, initially for one million users, National Payments Corporation of India said on Friday.

“Currently, NPCI has given its consent to roll out WhatsApp BHIM UPI beta launch with limited user base of 1 million and low per transaction limit,” the organisation said in a statement. “Four banks will join the multi-bank BHIM UPI model in phases [in the coming weeks] and full feature product shall be released after the beta test is successful.” At present, ICICI Bank processes the fund transfers.

The NPCI said that WhatsApp has to follow the “broad principles for interoperability”.

WhatsApp launched a limited payments service in India, where it has more than 200 million users, last week, Reuters reported. It facilitates payments using customers’ phone numbers, which are linked to their bank accounts.

WhatsApp is entering a competitive market and would compete against Google’s payments app and Paytm, which has the backing of Alibaba and SoftBank.

Paytm has expressed misgivings about WhatsApp Payments, with its CEO Vijay Shekhar Sharma saying that Facebook was “killing beautiful open UPI system with its custom close garden implementation”, NDTV Gadgets reported. He later clarified that this tweet was about the NPCI allowing WhatsApp integrate UPI payments without putting in place the safeguards that other payments apps had to incorporate.

“All apps so far had to adhere to a process by the NPCI, to create a smooth, interoperable experience that is not being required of WhatsApp,” Paytm’s Senior Vice President Deepak Abbot told NDTV Gadgets on Friday. “A Paytm user cannot send money to a WhatsApp user. The NPCI needs to look at this, they are locking the consumer.”

The NPCI is a private entity that consortium of banks runs. This consortium operates the UPI and other financial products, and acts as a regulator for the payments industry.