Thank you for reaching out to the Community! I’m happy to provide some assistance with the shop’s checkout to ensure this gets resolved.
As you work on building your shop, a ‘preview’ feature is available that allows you to see how products and/or themes look before actually being published. This feature however, is not intended for customers as a special link is created and functions in a slightly different way.
Due to this, I would recommend confirming that both your products and theme have been successfully published. You can also check that the URL is associated with your domain and not a preview link.
If after confirming this, you continue to receive that checkout error please feel free to Contact Support. This will allow our advisor team to investigate further and get this resolved as quickly as possible.
Please let me know if you have any other concerns.