Custom block not saving

I've created this block:

add_filter('rwmb_meta_boxes', function($meta_boxes) {
  $meta_boxes[] = [
    'title'           => 'Notice',
    'id'              => 'notice',
    'description'     => 'A notice block for emphasising spoiler alerts or providing updates',
    'type'            => 'block',
    'icon'            => 'megaphone',
    'category'        => 'layout',
    'keywords'        => ['spoiler', 'update'],
    'render_template' => get_template_directory() . '/functions/custom-blocks/notice.php',
    'supports'        => [
      'align' => ['wide', 'full'],
    ],

    // Block fields.
    'fields'          => [
      [
        'type'    => 'select',
        'id'      => 'type',
        'name'    => 'Type of notice',
        'options' => array(
          'spoiler' => 'Spoiler',
          'info'    => 'Info / Update'
        )
      ],
      [
        'type' => 'text',
        'id'   => 'headline',
        'name' => 'Headline',
      ],
      [
        'type'    => 'wysiwyg',
        'id'      => 'content',
        'name'    => 'Content',
        'raw'     => false,
        'options' => array(
          'textarea_rows' => 4,
          'teeny'         => true,
        ),
      ]
    ],
  ];

  return $meta_boxes;
});

It seems to work fine inside the editor. I'm able to add the block and edit fields. However, after updating the post and then refreshing the page, the inputted data is no longer there. It's not actually saving the field data.