Mostly Checkout Form Layouts are developed in the same way as standard CMS Form Layouts, with a few differences included below:
This liquid include used to output payment fields in a checkout form.
You should include this in the layout file for a checkout form at the position in the layout where you would expect the card payment elements to appear.
Outputting 1 payment gateway option
This will output the Payment Gateway that you most recently updated in Siteglide Admin.
Outputting multiple payment gateway options
This will output the Payment Gateway with the ID you select. When outputting by ID, you should select which is the default option.
Once you've added multiple Payment Gateways to your form using the include above, you can add JavaScript to switch between them on the client side: