How to enable Dynamic checkout buttons

Dynamic checkout buttons are an addition to the  Add to cart button on your product pages. 
With dynamic checkout buttons, customers can skip the cart and go directly to the checkout. Customers can choose to check out with Shopify, or with another familiar accelerated checkout method. This helps to speed up the payment process and lets customers check out using a method that they're comfortable with. Check out this Shopify Article to learn more about the benefits and restrictions of this feature.

Show dynamic checkout buttons on your products

From your Shopify admin, go to Online Store > Themes. Find the theme that you want to edit and click Customize
Click on the Theme settings tab and scroll down to the Products subsection

Here you will find options that are shared across all products in your store which will include, Product pages, Homepage Featured products and any Quick view modals that might exist in the theme.
Locate the Show dynamic checkout button settings and click to enable.

Click Save when done to apply the change.