System environment: Ubuntu system php apache2 mysql

Problem: All asynchronous methods in the browser post, get, etc. system do not execute callbacks. The code running on server2008 is normal, and the server receives the request data. , and after executing the PHP code, exit(json_encode returns to the front end. You can also see the returned json data in the console, but the callback is not executed. I would like to ask if there are any missing modules in my Linux that are not installed or configured somewhere.