PHP error log does not log when calling AJAX PHP script

I have a problem with PHP error log creation. The error log prints fine when
i access my index.PHP which contains just phpinfo() function to try out the error logging.

However when I’m using AJAX to forward Javascript request to .PHP page, the PHP error
logging does not work.

I have this javascript function on my index.html:

ajax_request.open(‘POST’, ‘search_foodinfo.php’);

On the browser dev tools it says that the POST function succeeded:

enter image description here

In the /var/log/apache2/error.log there’s no new row appearing. New row appears correctly when running index.php with phpinfo() function on it, but not with this POST request. What could be the problem? I’m using the PHP error logging functionality to debug my software in development.