WordPress中找不到选项页面

Question

我不断得到

  

错误：找不到选项页

当尝试保存我的插件管理设置时。
请帮忙。

我正在关注a tutorial online，了解如何在WordPress中进行管理员设置并使用输入的值。

我遵循第一种方法，但出现此错误

我在网上找到了一些答案，但它们含糊不清，而且我不太了解。
我正在使用WordPress v5.1.1和localbyflywheel

<?php 

/*
    Plugin Name: Smashing Fields Plugin
    description: >-
    Setting up configurable fields for our plugin.
    Author: Matthew Ray
    Version: 1.0.0
*/

class Smashing_Fields_Plugin {
    // Our code will go here
    public function __construct() {


    // Hook into the admin menu
    add_action( 'admin_menu', array( $this, 'create_plugin_settings_page' ) );

    add_action( 'admin_init', array( $this, 'setup_sections' ) );

    add_action( 'admin_init', array( $this, 'setup_fields' ) );


    }

    public function create_plugin_settings_page() {
    // Add the menu item and page
    $page_title = 'My Awesome Settings Page';
    $menu_title = 'Awesome Plugin';
    $capability = 'manage_options';
    $slug = 'smashing_fields';
    $callback = array( $this, 'plugin_settings_page_content' );
    $icon = 'dashicons-admin-plugins';
    $position = 100;

    add_menu_page( $page_title, $menu_title, $capability, $slug, $callback, $icon, $position );

    }


    public function plugin_settings_page_content() { ?>
    <div class="wrap">
        <h2>My Awesome Settings Page</h2>
        <form method="post" action="options.php">
            <?php
                settings_fields( 'smashing_fields' );
                do_settings_sections( 'smashing_fields' );
                submit_button();
            ?>
        </form>
    </div> <?php
    }



    public function setup_sections() {
    add_settings_section( 'our_first_section', 'My First Section Title', array( $this, 'section_callback' ), 'smashing_fields' );
    add_settings_section( 'our_second_section', 'My Second Section Title', array( $this, 'section_callback' ), 'smashing_fields' );
    add_settings_section( 'our_third_section', 'My Third Section Title', array( $this, 'section_callback' ), 'smashing_fields' );
    }


    public function section_callback( $arguments ) {
    switch ( $arguments['id'] ){
        case 'our_first_section':
            echo 'This is the first description here!';
            break;
        case 'our_second_section':
            echo 'This one is number two';
            break;
        case 'our_third_section':
            echo 'Third time is the charm!';
            break;
    }
    }

    public function setup_fields() {
    add_settings_field( 'our_first_field', 'Field Name', array( $this, 'field_callback' ), 'smashing_fields', 'our_first_section' );
    }

    public function field_callback( $arguments ) {
    echo '<input name="our_first_field" id="our_first_field" type="text" value="' . get_option( 'our_first_field' ) . '" />';
    register_setting( 'smashing_fields', 'our_first_field' );

    }
}
new Smashing_Fields_Plugin();

?>