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I got the scratch card. And the promised cashback of Rs.30!
1) I did it in the app
2) I had device location turned off. After the payment completed, once the control was in the 'payment successful' page, the app asked for the device location to be turned on (through a device pop-up message; not app message). I clicked 'No Thanks' in the pop-up message displayed by my phone.
3) After a few seconds, to my surprise, the Scratch Card popped up in the payment successful page, scratching which revealed the cash back of Rs.30.