If you already have a list of subscribers that should receive a unique code there are two ways you can solve it. Either you use our Redeem Link feature to add a custom link to your email that your subscribers use to redeem their unique code. If this is a one time thing you don’t need to use our app. You can solve it by manually importing the codes to your list and then send out a campaign with the codes using a merge tag. Shopify has written a guide (Include discount codes in your MailChimp newsletter) that shows how to do this.