Displaying PHP Errors from admin-ajax.php in Wordpress 4.9+

open up the wp-includes/load.php

if ( defined( 'XMLRPC_REQUEST' ) || defined( 'REST_REQUEST' ) || ( defined( 'WP_INSTALLING' ) && WP_INSTALLING ) || wp_doing_ajax() ) {

        @ini_set( 'display_errors', 1 );

    }