Sorry forgot to update, nope I didn't get points for the transaction for Amex Bill pay from IDFC tap 🙁
I started using SBI virtual card for Amex Payments for 2% rewards
I paid my Amex bills in instalment for 4 * 50000 and got 500 Rewards and 500 Bonus points for each 50000 (4000 as reward points for 2L bill)