It might be showing lesser amount than what it is showing on other apps, right? It might be because you have some arrears in your bill.
This is experimental -
I had faced this issue when I was not using Amazon pay long before to pay electricity bill.
Try paying bill for the lesser amount on Amazon. Check after few days. If the bill settlement is reflected in Amazon, then you might be able to pay any custom amount against your electricity bill and therefore pay the remaining amount. If the same bill amount still keeps reflecting then pay the same bill amount again, the additional amount paid will be adjusted in your next bill cycle.
Attaching screenshot here where I can pay any custom amount on my Amazon pay after the bill is settled but this is for bescom (Bangalore electricity)
