Which remittance platform able to provide the lowest fee by paying using a credit card/debit card?

It may not be considered as qualifying spend for most cards

I should think Revolut will be your answer. I tried this app recently and my understanding from a friend who introduced it to me is that there are no fees. You just need to under stand what are the T&Cs of your particular promotion, i.e. what counts as qualifying spend, whether you earn miles on it or not. If it counts as qualifying spend, then by all means go for it, especially if the sign up bonuses was what made you sign up in the first place.