Hey Matt,
Thanks for reaching out. Coupon codes are a feature of the eCommerce plugin that you choose to use, not The Events Calendar itself or any add-ons for The Events Calendar.
So, for example, if you wanted to use WooCommerce on your site, then The Events Calendar: WooCommerce Tickets would enable ticket sales; but WooCommerce itself would allow and power the coupon codes on your site. In this example, then, WooCommerce’s own documentation on this topic would be the best resource → https://docs.woothemes.com/document/coupon-management/
I hope this information helps; let me know!
— George