Shopify has deprecated checkout.liquid. To add loyalty features to your checkout pages, use our Checkout extensions.
If you're a Shopify Plus store, you may need to enable your checkout.liquid layout before certain LoyaltyLion features can be installed.
In the Shopify Admin, navigate to your Online Store > Themes page
Click on the menu icon of your active theme and click Edit code
Click "Add a new layout" under the Layout menu
Note: if you already see acheckout.liquidlayout here, you don't need to do anything. Only follow the rest of the steps if you don't already have acheckout.liquidlayout in the list.
In the drop down list, select "checkout" and press "Create layout"
Note: if you don't see an option "checkout" in the drop down, we will need to ask Shopify to enable the feature for you.
The new layout should be created successfully, and you should now see it in the list