Steps to add popup messaging to your BigCommerce store
Login to your account here, and click on the website where you want to enable our on-site messaging.
Click on Integrate in the left menu.
Login to your BigCommerce Admin Panel.
Click on Storefront from the left sidebar menu.
Then, choose Script Manager. Type the name of script which you can identify later, e.g. PushAlert Onsite Messaging.
Set location as Footer, and All Pages for where it should be added.
Set Script Category as Functional and Script Type as Script.
Paste the copied script in the Script Contents section and click on Save.