FLEX credits will never expire. You can use for any store or any task (as long as it falls within the scope of our small task service) in the future. You can find more details about the FLEX credits in the article below.
PRO credits expire when your subscription is cancelled. If you have any left over task credits from your monthly subscription they will expire when your subscription cycle ends.
However, if you have purchased additional task credits (for $39 per task) while you were subscribed to the PRO plan, those task credits would remain on your account after cancellation. You can find more details about the PRO plan in the article below.