Checkouts will occur at the shop domain instead of checkout.shopify.com
API
Effective July 20, 2017
We're making changes to checkout domains for all Shopify stores. Rather than the checkout domain being checkout.shopify.com, checkout will occur on the shop domain that the customer is shopping on.
For example, where the previous checkout URL format was https://checkout.shopify.com/#{shop.id}/checkouts/#{checkout.token}, the new format will be https://#{shop_domain}/#{shop.id}/checkouts/#{checkout.token}.
If the merchant forces redirects to their primary shop domain, then all checkouts will occur on the primary domain.
We don’t anticipate any major breakages for existing Shopify apps. However, if your app relies on parsing the checkout URL for any reason, then the checkout domain is no longer guaranteed to be static so you will need to anticipate this.