Hi, Jessica.
We do not provide support for WooCommerce or its coupons, cart, checkout, payment gateways, etc.
The best I can suggest is making sure your coupon doesn’t have rules for being active on a specific product or price amount that maybe it is actually performing how it was told to. You might also check if any coupons work on other products (i.e. non-tickets products).
Sorry I can’t be of more help here, but you might be able to contact WooCommerce support.
Please let me know what you find out.
Thanks.