How to fix this Add Media Button not working issue
1-Open the wp-config.php from root wordpress directory.
2-Find this code in it.
require_once(ABSPATH . 'wp-settings.php');
3-add the following code before the above code.
define('CONCATENATE_SCRIPTS', false );
*Script concatenation in admin area is normal behavior.
4-Save that file and check that button.If you’re already open that error post page reload that page for the check the button.
Still not fixed ?
1-Disable all plugins.Don’t afraid.Each Plugin settings are not resetting.Then check then it’s working or not.
2-Try to switch current theme to wordpress defalut theme.
3-If you are using cache plugin, clear the all cache with admin panel cache too.
4-If you are using minify plugin, clear the cache and disable that plugin and check for the button.
Now should be working the “Add Media” button.