If you happen to go through your campaign and when you get to the coupon, it shows as expired, most likely, you have set an outdated coupon expiration date. You can check this by editing the campaign and going to Step 4 (Emails/Text) then open up the Coupon Settings tab and check if there's a coupon expiration that's already outdated.

The coupon will normally show expired in that case.

If you didn't set a coupon expiration, please reach out to support so they can have a better look.