A Dynamic checkout button is an option that allows your customers to quickly buy the product they're viewing.
This function works by ignoring the usual route a Shopify transaction would take - through the theme's cart page and then the Shopify platform's Checkout page.
This is skipped completely and the transaction is instead loaded through the checkout system of the chosen payment gateway, for the operation of collecting payment and organising Shipping details.
The button in question changes in appearance to match the linked system's branding - this is decided by the Payment System themselves and is not something that the theme has any direct control over.
Within your theme, the button is displayed next to the Add to cart button and can be used to buy only single variants of a product - a customer can use a dynamic checkout button to buy two red t-shirts, but not a red t-shirt and a blue t-shirt, as an example.
It will also appear within the cart page itself, next to the Place your order button that would usually start the Shopify payment system > Checkout process, to offer an alternative choice at the last step to customers.
The checkout method that's displayed on the button depends on a few factors:
your payment settings, activated for your storefront
the customer's browser
the customer's device
the customer's personal payment history
the version of the theme you're working with
So the appearance of these buttons is not entirely controlled by the theme but can change organically depending on the other factors involved.
Additionally, there are positive and negative factors linked with enabling these buttons which you should consider when setting up your storefront:
Enables quick routes to immediate purchases.
Enables more options, to suit a wider customer base - Some customers will prefer to stick to a trusted or accessible payment system.
Allows extra business functions, with some payment system providers.
Allows customers the ability to skip the Shopify payment system - some Shopify apps and Shopify Automatic Discounts rely on this system being used for the transaction, so this could affect your storefront's functionality.
Not customisable, beyond changing the colours of Shopify's own Unbranded button
With more modern versions of our themes - Flow 11.4.5 and later - this will automatically be enabled on your storefront, as part of an update made to the Shopify Platform.
For working with an older theme version than this will have to have these manually enabled if desired.
For Flow, navigate to:
Online Store > Themes > Customise.
Using the upper Template Selector drop down to jump to 'Product page' and picking the same entitled option, on the left sidebar.
In this menu, scroll down and use the 'Show dynamic checkout button' toggle present here.