Please check the following:
- The app is active on your published theme. Open the Installation page in the app and make sure your published theme shows Active.
- The term is turned on. In the app Dashboard, the toggle next to the term should be on.
- The product is assigned. Open the term and check Assigned products and the exclusions.
- The button is enabled. On the Options For Dynamic Checkout tab, make sure the button you're testing is turned on.
If everything is set and the checkbox still doesn't appear, please grant us access to your store admin (the Themes and Apps sections) so we can check what's wrong: send a staff invitation to support@nexusmedia-ua.com and let us know once it's done. We can also send you a collaborator request if you prefer.