Why would Paytm be having any problem with crypto companies? All they are doing is advertising for CoinDcx and charging a commission from them, the voucher that you got was given by CoinDcx and would be redeemed too by coinDcx only so Paytm has no responsibility in that front. Moreover so far it's not illegal to do business with crypto exchanges, also when big tv channels and even IPL are partnering with crypto exchanges, I don't think Paytm would like to lose any such opportunity, this is the reason you got CoinDcx voucher on these payments.