Project Fi referral program was supposed to end on Jan. 11 but Google extends the promotion to an indefinite schedule.

For current users of Google's Project Fi, they can still invite other potential users to join register to the platform and get a $20 gift as credit.

The referral program works as easy as referring the service to others and once they join, both parties can receive the extra credit. As a carrier service, Project Fi offers data service on three mobile networks but only connects to the strongest signal, according to Android Central.

The service works like this - it searches for the strongest signal between selected mobile carriers, either T-Mobile, US Cellular, Sprint or Wi-Fi.

Oh, hello @FlySJC and the free @projectfi swag kiosk! (They're playing cards) #FlyWithFi pic.twitter.com/JkrSQ3VDko

— Jake Wharton (@JakeWharton) January 9, 2017

The Referral program has started since December 2016 and it should be able to lure more potential customers to enjoy the benefits. And the reason behind the extension is due to the huge response that Google has received so far.  

About Project Fi

Google Project Fi is currently available in more than 130 countries. The prepaid billing offers one-month cycle with benefits like unlimited messaging for $20 per month.

#google Project Fi Subscribers Can Now Avail High-Speed.... #hrtechnology #tech #gadgetspic https://t.co/Cq6lhBx7oY pic.twitter.com/giLafLJmNb

— Gary Feng (@garyfengg) January 15, 2017

There's only a few devices compatible for Fi, according to Android Headlines. Project Fi can be used by Google supported handsets including Nexus 6P, Nexus 6 and Google Pixel phones.

For every user, there is a unique referral code that they can distribute to potential subscribers up to 10 persons. This code can be found in within the app or the website. It goes the same to check the total credits received. Other condition includes requiring new subscribers to keep the account active for 30 days with two-month payments service.