SQL -> JSON -> HTML not displaying on InfinityFree

I have updated the password to your hosting account to a new random password. Please keep in mind that this is a public forum, so anything you post here can be seen by anyone. So you must make sure to never share any confidential data, which especially includes passwords.

As for the issue itself, I checked your page, and in both the Network tab and the Console tab in the browser Developer Tools, I see the book_fetcher.php page responds with a 500 Internal Server Error. This usually means that the PHP code crashed. I don’t see anything immediately wrong with it, but this is how you can start troubleshooting it yourself: