Just bought a Costco membership on Groupon. I entered the email I used to register before, which expired more than 18 months ago, and only afterward did I see online DP saying you might need a new email?
Can I still use the email I previously registered with? Or do I absolutely have to find a way to change the email to trigger the $45 gift card they send?
When you say "new email," do you mean an email address that has never been used to register with Costco? If it was only used to sign up before but never linked to a membership, it may not count as completely new. Also, Groupon's terms are usually very detailed, so it's best to check the email to confirm whether the gift card trigger condition applies to new members or new email addresses—that way you'll be more confident when asking customer service.
I don't think using an old email is necessarily a problem—Groupon probably only cares about your Groupon account, and the email tied to your Costco account likely doesn't matter much.
If that doesn't work, can I change the email address linked to my Groupon account?
I'd suggest first checking with the Costco membership counter or online customer service to confirm the specific terms of this promotion, and ask clearly whether the gift card is issued based on the Groupon order number or the Costco registered email. At the same time, keep your Groupon purchase receipt and screenshots of the terms, so that if you don't receive it, you can use the evidence to file a complaint. Don't rush to repurchase or switch email accounts.
Any updates? What did customer service say?