If you already have certificate credits - no they will not expire.
In summer of 2017, Accredible's pricing moved towards a pricing plan model to simplify billing, allow better tracking of your usage, and saves you money when you are issuing many credentials a year. If you purchased Credential Credits with Accredible before August 2017, they will still be in your account and we will continue to support the purchase of those credits until you decide to switch to one of our new plans. Everything you need to maintain your credits should be available in the billing section of your account settings, and you can contact support for any help or purchase requests.
You may want to consider switching to a new pricing plan when old credential credits are used up. The unit cost on even the smallest plan is much cheaper than purchasing credential credits was. You can see our full pricing table here