IndiGo — ticket purchasing

I want to purchase tickets for my family by credit card through website, but I am not a part of travelling. So, when I asked al rais travels they said I can't purchase for them. So, please advise me I can purchase ticket for my family or not. During last travelling to India, I ask at airport one of your team member during check-in. He said I can purchase and the traveller should bring the copy of credit card. So, please advise me I can purchase the ticket are not.