1% only as Paytm is not an Apay partner merchant. Also Paytm will charge you convenience fees if you pay electricity bill via credit card. In fact Paytm is now charging extra for all transactions done via Paytm using credit card.
Apay also has a limit of 15K in single transaction for bill payment.
Best is to use discom's website where charges will be pretty low & you will get 1% in amazon card.