<?php
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

global $wpdb;

$user_id = get_current_user_id();
$table   = $wpdb->prefix . 'wppm_notifications';

$results = $wpdb->get_results(
    $wpdb->prepare(
        "SELECT * FROM $table
         WHERE user_id = %d
         AND is_read = 0
         ORDER BY created_at DESC",
        $user_id
    ),
    ARRAY_A
);

wp_send_json($results);