Only the footer in the checkout is visible when I try to load the checkout. What's wrong?

The most common reason for this error is a mismatch between the actual URL of your site and the checkout.url property of the Create payment method. This property is required when using an embedded checkout.

For an embedded checkout page, we will always validate that you are initializing the checkout on the URL that was provided. If the domains do not match, only the footer of the checkout will be loaded.