400 bad request admin-ajax file upload

Your action should be wp_ajax and wp_ajax_nopriv instead of admin_ajax.

 add_action( 'wp_ajax_new_message', array($this, 'process_upload') );
 add_action( 'wp_ajax_nopriv_new_message',array($this, 'process_upload') );

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)