To refer a friend for a Delta-branded credit card or any American Express card, visit the Refer-a-Friend website and log in to your account. Once you’re signed in, you can enter your friend’s email address and American Express will send them an automated email. Or you can generate a personalized referral link to share on social media. If your friends are interested, they can choose to apply for an American Express card. If they are approved, you’ll both receive an award.