Just need to make first call to get the reward.
you will get an email with instructions to get your reward. You can also redeem it by going into the Duo app, tapping More, and clicking on Redeem rewards.
The amount will be directly transferred to your linked bank account.
You can earn a maximum of 30 rewards, with a limit of Rs. 1,000 per scratch card.
How to refer?
Open the app.
click on the three dots on the upper right side of the screen
Click on invite friend option
Select a contact to invite
There will be lot of options to invite like whatsapp, facebook, Gmail,message etc, choose any one to get the referral link