Why are there errors when including files on an ajax request?

Question

PHP

I have the rewrite module enabled on the site, and files are connected via autoload , when I make a request via ajax it gives me an error .Uncaught Error: Class 'Db' not found blah blah blah Stack trace. Such a class was not found and some kind of stack trace, in short no idea. I understand that autoloads do not work, how to fix it or where to read about it