Login to your BigCommerce back office and navigate to Apps -> Ebizio Checkout.
Click Settings within the Ebizio Checkout application sidebar then navigate to the Enable Checkout tab.
Click the Enable Checkout button.
If you do not have the "Custom Checkout" option
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 System Requirements 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.