Hello, did you happen to upgrade any of your refines, or charms or anything of the sort? There is the option to use coupons if materials are insufficient, which can quickly deplete coupons, if you do not ensure this option to be turned off prior to upgrading. If this is not the case, CS can check to see if there are any discrepancies on your account. They would be the only place to help with missing coupons.

https://support-center.oasgames.com/