I'm about to send a campaign with multiple variations, each with a different unique coupon code, how many codes do I need to add ahead of time?
When a campaign has a unique coupon code within a template, Klaviyo will check the number of codes in the coupon against the entire list. The same holds true with a campaign, regardless of how many variations of the same email that used for the campaign. So, even if you're A/B testing a campaign that has multiple variations, each variation needs to have enough coupon codes to match the total list send, not just the amount of recipients for that variation.
For example, say you want to send a campaign to 5,000 profiles, but also want to A/B test the content in your email. If you have two different variations of a campaign, each with a separate, unique, coupon code, you would need to add 5,000 codes to each of those four unique codes.