Thank you for sharing the link, we reviewed the link and noticed the behavior of the plugin may have been modified by custom code or the theme.
As you can see in this quick video, we recreated your add-ons, 3 text based add-ons and 1 radio add-on. All required add-ons.
In the video, you can see, if all add-ons are not selected by the customer, an error is occurring showing the required add-on needs to be selected to be added to the cart. We also noticed on your site, the line items sub-total, add-ons total and total are not displaying.
A few recommendations.
– Review our video and verify you have setup the required settings correctly in the Product Add-ons options
– Review or revert any custom code modifying the plugin or product page behavior for Product Add-ons
Often a good step is performing plugin/theme conflict testing. It’s easy, disable all plugins except WooCommerce and Product Add-ons. Remove any custom code modifications and use the WooCommerce Storefront theme. This will help identify what is causing the conflict or code modification impacting the functionality from working correctly.