Install Fast Checkout Examples
NOTE: For legacy theme templates (Blueprint). You must include the following script tag in the HTMLHead.html file

AND remove cart_id="{{cart_id}}" from the Fast checkout button
<script src="https://js.fast.co/fast-bigcommerce.js"></script>
NOTE: Replace the app_id variables with your own app id. You can get this from your Seller Dashboard
Product Detail Checkout Buttons
Product detail page
Cornerstone location: /templates/components/products/add-to-cart.html

Blueprint location: Snippets/ProductAddToCart.html

Insert just above:
{{#or customer (if theme_settings.restrict_to_login '!==' true)}}
<!------ FAST CHECKOUT BUTTON START ----------->
<div class="fast-wrapper"></div>
   <div class="fast-or">OR</div>
   <fast-checkout-button app_id="REPLACE-WITH-YOUR-APP-ID"></fast-checkout-button>

<style></style>
   .fast-wrapper {
     padding-bottom: 20px;
     margin-bottom: 20px;
   }
   .fast-or {
       position: relative;
       top: 80px;
       background: white;
       width: 40px;
       text-align: center;
       margin-left: auto;
       margin-right: auto;
       color: #757575;
   }
   @media only screen and (max-width: 767px){
       .fast-wrapper {
           border-bottom: 1px solid #dfdfdf;
           border-radius: none;
           padding-right: 1%;
           padding-left: 1%;
       }
   }
   @media only screen and (min-width: 768px) {
       .fast-wrapper {
           border: 1px solid #dfdfdf;
           border-radius: 5px;
           padding-right: 20%;
           padding-left: 20%;
       }
   }



<!------ FAST CHECKOUT BUTTON END ----------->
Cart checkout buttons
Cart Preview overlay
Cornerstone location: /templates/components/cart/preview.html

Blueprint location: Snippets/FastCartThickBoxContent.html

Insert just below:
class="previewCartCheckout">{{#if cart.show_primary_checkout_button}}
<!------ FAST CHECKOUT BUTTON START ----------->
<div class="fast-overlay-wrapper"></div>
 <div class="fast-overlay-or">OR</div>
 <fast-checkout-cart-button cart_id="{{cart_id}}" app_id="REPLACE-WITH-YOUR-APP-ID"></fast-checkout-cart-button>

<style></style>
.fast-overlay-wrapper {
   clear:both;
   margin-bottom:20px;
   border-bottom: 1px solid #c1c1c1;
   padding-bottom: 20px;
}.fast-overlay-or {
   position: relative;
   top: 80px;
   background: #e5e5e5;
   width: 40px;
   text-align: center;
   margin-left: auto;
   margin-right: auto;
   color: #757575;
}



<!------ FAST CHECKOUT BUTTON END ----------->
Mini Cart Preview
Cornerstone location: /templates/components/common/cart-preview.html

Insert just above: <div class="previewCartAction"></div>
<!------ FAST CHECKOUT BUTTON START ----------->
<div class="fast-mini-cart-wrapper"></div>
 <div class="fast-mini-cart-or">OR</div>
 <fast-checkout-cart-button cart_id="{{cart_id}}" app_id="REPLACE-WITH-YOUR-APP-ID"></fast-checkout-cart-button>

<style></style>
.fast-mini-cart-wrapper {
   clear:both;
   margin-bottom:20px;
   border-bottom: 1px solid #c1c1c1;
   padding-bottom: 20px;
   margin-left: 20px;
   margin-right: 20px;
}.fast-mini-cart-or {
   position: relative;
   top: 80px;
   background: white;
   width: 40px;
   text-align: center;
   margin-left: auto;
   margin-right: auto;
   color: #757575;
}



<!------ FAST CHECKOUT BUTTON END ----------->
Mini Cart Page
Cornerstone location: /templates/pages/cart.html

Insert just below: {{#if cart.show_primary_checkout_button}}

Blueprint location: Panels/CartContent.html (below <div class="ProceedToCheckout">)</div>
Checkout Page
<!------ FAST CHECKOUT BUTTON START ----------->
<div class="fast-wrapper"></div>
<div class="fast-or">OR</div>
<fast-checkout-cart-button cart_id="{{cart_id}}" app_id="REPLACE-WITH-YOUR-APP-ID"></fast-checkout-cart-button>

<style></style>
.fast-wrapper {
clear:both;
margin-bottom:20px;
border-bottom: 1px solid #dfdfdf;
border-radius:none;
padding-bottom: 20px;
}
.fast-or {
   position: relative;
   top: 80px;
   background: white;
   width: 40px;
   text-align: center;
   margin-left: auto;
   margin-right: auto;
   color: #757575;
}
@media (min-width: 551px) {
   .fast-wrapper {
       margin-left: auto;
       margin-right: 0;
       width: 100%;
       border: 1px solid #dfdfdf;
        padding-left: 10%;
        padding-right: 10%;
        padding-bottom: 20px;
        border-radius: 5px;
   }
}
@media (min-width: 801px) {
   .fast-wrapper {
       width: 50%;
   }    
}
@media (min-width: 1261px) {
   .fast-wrapper {
       width: 50%;
   }
}



<!------ FAST CHECKOUT BUTTON END ----------->
Main Checkout Page
Cornerstone location: /templates/pages/checkout.html

Blueprint location:

Insert just before: {{{ checkout.checkout_content }}}
<!------ FAST CHECKOUT BUTTON START ----------->
<div class="fast-wrapper"></div>
 <div class="fast-or">OR</div>
 <fast-checkout-cart-button cart_id="{{cart_id}}" app_id="REPLACE-WITH-YOUR-APP-ID"></fast-checkout-cart-button>
<style></style>
.fast-wrapper {
   clear: both;
   margin-top: 40px;
   margin-bottom: 20px;
   padding-bottom: 40px;
   padding-top:20px;
}
@media (max-width: 799px) {
   .fast-wrapper {
       margin-left: 8%;
       margin-right: 8%;
       margin-bottom: 20px;
       border-bottom: 1px solid #dfdfdf;
       border-radius: none;
       
       padding-right: 12%;
       padding-left: 12%;
   }
}
@media (min-width: 800px) {
   .fast-wrapper {
       margin-left: auto;
       margin-right: auto;
       margin-bottom: 20px;
       border: 1px solid #dfdfdf;
       border-radius: 5px;
       
       padding-right: 25%;
       padding-left: 25%;
   }
}.fast-or {
   position: relative;
   top: 100px;
   background: white;
   width: 40px;
   text-align: center;
   margin-left: auto;
   margin-right: auto;
   color: #757575;
}



<!------ FAST CHECKOUT BUTTON END ----------->
Also need to add this script in script manager with settings:

- Location: **Footer**

- Pages where script is added: **Checkout**

- Script category: **Essential**

- Script type: **Script**
<script type="text/javascript"></script>
   var oldOnload = window.onload;
   window.onload = function () {
     if (typeof oldOnload == 'function') {
       oldOnload();
     }
   const fw = document.getElementsByClassName("fast-wrapper")[0];
const lm = document.getElementsByClassName("layout-main")[0];
lm.prepend(fw);
   }