I pay my Tata Neu Plus Rupay card bills on Amazon itself. Weird that Regalia shows as "unsupported" for you. Check if you are able to pay elsewhere like Paytm or Mobikwik.
I went ahead and added the card in spite of it saying unsupported.
Now it is displayed as Discover card (instead of VISA/MASTERCARD etc.). Is that how it appears for Rupay cards?