If you have installed Convify app for BigCommerce and see message like this 
it means you need to add pixel code manually, if you don't see this message - your store is build on Stencil theme engine and code were added automatically.
If you have custom theme and for some reason automated integration failed, you can add pixel code manually?
1. In your Convify account on Campaigns page click on View Code button and copy the code OR you can just copy this line of code <script async src="//cdn.convify.com/js/pixel.min.js"></script>
2. Visit your BigCommerce store, select Storefront -> Footer Scripts and paste a code, if you have any other scripts there, paste Convify pixel code at the end.
3. Press Save button at right bottom corner.