Short answer; it depends.
Please note you must be 18 years of age or older and a legal resident of the United States with a good credit score.
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If your looking for the application page for the Citi Diamond Preferred credit card please visit www.citi.com/lovediamondpreferred and follow the onscreen instructions.
Please note if you received your certificate via email, simply print the email containing your reward certificate, or show it on your mobile device, at any U.S. or Puerto Rico Costco warehouse by December 31 of the year it was issued.