I also got an email today on my active account with 4 credits. It's a spend 3 credits, get a $10 coupon. Purchases have to be made by June 26.
Details:
You received this offer because you had at least 3 credits in your account as of June 21, 2017. You must use 3 or more credits between June 23 and June 26, 2017 @ 11:59 PM PT (US) to be eligible for the $10 coupon. The promotion applies only to items sold by audible.com. The same items sold by other sellers (e.g., audible.co.uk) do not qualify. Coupons cannot be resold, transferred for value, redeemed for cash or applied to any other Audible account, except where required by law. This promotion may not be combined with other offers. An Audible account is required to be eligible for this promotion. Limit one reward per customer. Your coupon for $10 will be dropped into your account no later than June 30, 2017. The coupon will expire on August 1, 2017. Other terms and conditions apply, including those available here:
here. If you violate any of the terms or conditions, the promotion will be invalid, and the offer will not apply. Audible reserves the right to modify or cancel at any time. Void where prohibited.