You can add an authorized user to your Amex Platinum Card over the phone or online.
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If you add a Companion Card, your authorized user won't enjoy perks but can help you earn points and spend some of your annual credits. If you add an additional Amex Platinum, there's a fee, but your cardholder will enjoy the perks discussed below. Enrollment is required for select Amex benefits.
You may purchase guest access for your spouse or domestic partner and a child under 21, or up to two other traveling companions for $29 per person. Any additional guests may purchase One-Day Passes.