Enabling shop pay on your checkout links
When creating links, you can specify the checkout type to direct the customer to Shopify Checkout.
If you would like all of your checkout links to navigate to Shop Pay checkout, navigate to preferences and click on Enable checkout powered by Shop Pay.
Now all your checkout links will re-direct to Shop Pay app if it has been enabled on your store. If you do not have Shop Pay enabled, check out this Shopify help doc on how to activate Shop Pay on your store: Activate Shop Pay