Hey @2385861858,
I followed the steps and I see that it doesn’t work in your site. It looks like a third party plugin conflict because I tested the “apply to coupon” button in my test site (without third party plugins and customizations) and it works out of the box. Would you mind testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
If you do have template customizations and custom Javascripts and additional functions in your your functions.php, please remove them also.
Please test the “apply to coupon” without any plugin and customization.
We need to know if this issue is really caused by X. Sometimes, simply switching to another theme does not mean that X is causing the issue because the custom functions are not used and the widgets reset. But, it is a step forward in troubleshooting.
Thanks.