This usually happens when you switch from V2 to V3 checkout pages for your site.
The error message shows up on your Live site when you click on the preview option (Configure Chargebee). This is because the setting Preview gets the data from the Test site and displays the Checkout page. This is to ensure that the Live site data is not tampered with.
Since there is a version mismatch between your Test site and the Live site earlier, you are getting this error.