Add AJAX infinite scroll to my website

I have a custom-built (i.e., it is not a standard CMS) website built 10-15 years ago in PHP. The site was recently converted to run on PHP 7.2. The website has something like 400,000 pages on it; each page is generated from the database backing the website. I want AJAX infinite scroll added to one particular section of the website. For the primary table in the database that holds the page content, I added a column called next_url. The next_url column contains the relative URL that I want to be AJAX-loaded next. If the field value is NULL, then nothing should be loaded next. I want you to use the infinite scroll library ([login to view URL]), and whatever additional PHP you need to write to load page after page after page according to the value of next_url (next_url is in the array returned from the database at page generation time). I also want you to have infinite scroll change the URL in the browser as the user scrolls to the next page (that is a feature of the [login to view URL] library). I want you to load the next page when the current page is scrolled down 50% in the browser. I will spin up a non-production EC2 instance for you to add this functionality to the website/codebase. I will provide you a PEM key file to SSH into the machine. I have a pretty good understanding of the codebase and will tell you exactly where the relevant PHP files are located for this section of the website.