Login to your BigCommerce back office and navigate to Advanced Settings -> Checkout.
Change the "Checkout Type" to be "Custom Checkout".
Scroll down to the "Custom Checkout Settings" and set the "Script URL" to be https://cdn.ebizio.com/ebizio-checkout/storefront/auto-loader.js.
Check the box stating that "This checkout supports Optimized One-Page Checkout settings". This is required for the checkout to work properly.
Click "Save" to the bottom right
If you do not have the option to enable a Custom Checkout, you will first need to have the "Optimized One-Page Checkout" active on your store. Typically, once you enable this option you will see "Custom Checkout" as a choice.
note: if "Optimized One-Page Checkout" isn't already active, please read item #2 here as there are some considerations to make prior to switching.
If "Optimized One-Page Checkout" is currently active and you still do not see "Custom Checkout" as a choice, please submit a support ticket we can put in a request with BigCommerce.