Use SBI CB to buy Amazon Pay Gift card from Amazon or tata neu or park. You get 5%.
Go to magicpin. Firstcry vouchers are available at 6% discount. Buy it using Amazon pay option. So you get around 10-11% totally.
Remember that firstcry vouchers are one time usable. If you want to purchase for 1050 INR, buy 1000 rs voucher and then pay thr rest through any other payment method. SBI CB fetches 5% on firstcry