Thêm function:
function checkUserIDFacebook($userID) {
    global $wpdb;
    $user = $wpdb->get_results("SELECT * FROM wp_nicmsusermeta WHERE  meta_key =  'open_type_facebook' AND meta_value= $userID ");
    return $user;
}

function existsEmail($exists) {
    if(get_user_meta($exists, 'open_type', true) == 'facebook,') {
        $this->checkContent($exists);
        $status = $this->isUserInfoValid($exists);
        $token = $this->set_token($exists);
        if($status == 1) {
            $data = array(
                'status' => 1,
                'token' => $token
                );
            return $data;
        }
        $data = array(
            'status' => 0,
            'token' => $token
        );
        return $data;
    } else {
        return new WP_Error( 'rest_not_found', __( 'Email already exists.', 'wpuf-pro' ), array( 'status' => 404 ) );
    }
}

function notExistEmail($user, $url, $access_token) {
    if (!isset($user['email'])) {
        $user['email'] = '';
    }
    $username = 'FACEBOOK'.$user['id'];
    $password = wp_generate_password( 20, false );
    $creationResult = wp_create_user( $username, $password, $user['email'] );
    if ( is_wp_error( $creationResult ) ) {
        return new WP_Error( 'registration_failed', __( 'Registration failed.' ), array( 'status' => 422, 'message' => $creationResult->get_error_message() ) );
    }
    $user_img = open_connect_http($url.'/me/picture?redirect=false&height=320&type=small&width=320&access_token='.$access_token);
    $img = $user_img['data']['url'];
    if(isset($img)) {
        $imagesID = $this->saveImageFromUrl($img);
        update_user_meta($creationResult, 'images', $imagesID);
        $image = wp_get_attachment_image_src($imagesID, 'avatar-thumb');
        update_user_meta($creationResult, 'user_avatar', $image[0]);
    }
    $name = $user['name'];
    update_user_meta($creationResult, 'nickname', $name);
    update_user_meta($creationResult, 'gender', $this->gender($user));
    update_user_meta($creationResult, 'open_type', 'facebook,');
    update_user_meta($creationResult, 'open_type_facebook', $user['id']);
    update_user_meta($creationResult, 'open_img', $img);
    update_user_meta($creationResult, 'open_access_token', $access_token);
    update_user_meta($creationResult, 'deactive_user', 1);
    $test = get_user_meta($creationResult , 'user_avatar', true);
    $token = $this->set_token($creationResult);
    $data = array(
        'status' => 1,
        'token' => $token
    );
    return $data;
}

------------
Search: function doLoginFacebook Sửa thành:
public function doLoginFacebook($request) {
    global $wpdb;
    $access_token = $request['access_token'];
    $appID = '801820409985344';
    $appsecret = 'e97f2f8b0612369b1eaf605d46e6e018';
    $url = 'https://graph.facebook.com';
    $user = open_connect_http($url.'/me?fields=id,name,email,gender&access_token='.$access_token);
    $idUser = $user['id'];
    if(!isset($idUser)) {
            return new WP_Error( 'rest_not_found', __( 'User not found.', 'wpuf-pro' ), array( 'status' => 404 ) );
    }
    $email = $user['email'];
    if($email != '') {
        $exists = email_exists($email);
        if($exists) {
            return $this->existsEmail($exists);
        } else {
            return $this->notExistEmail($user, $url, $access_token);
        }
    } else {
        $checkUser = $this->checkUserIDFacebook($idUser);
        if(count($checkUser) > 0) {
            return $this->existsEmail($checkUser[0]->user_id);
        } else {
            return $this->notExistEmail($user, $url, $access_token);
        }
    }
}