Every time a coupon is applied to an order, a copy of the entire coupon object is stored as part of the order metadata. This causes the database space used by WooCommerce to grow tremendously in stores with heavy coupon usage. There is an open issue regarding this here.
How to provide feedback
To help us decide how to move forward, we have now also opened a discussion in GitHub about a possible solution.
Please comment your thoughts and opinions in the GitHub discussion.
Who does this affect?
If you use the WooCommerce REST API to retrieve order details, and you use the part of the retrieved data that describes applied coupons, then this change may be relevant to you. We would love your feedback.
We aim to take a decision about further steps regarding this in early December 2023. Thanks for your participation!