wp-create-metabox-array.php

<?php

add_action('add_meta_boxes', function() {
  add_meta_box('metabox_name', 'Metabox Title', 'metaboxCallback', array('post', 'page'), 'normal', 'default');
}, 1);

function metaboxCallback($post) {
  $value1 = get_post_meta($post->ID, 'meta_prefix_'.'meta_field_name_1', 1);
  $value2 = get_post_meta($post->ID, 'meta_prefix_'.'meta_field_name_2', 1);
  ?>
    <input type="text" name="meta_prefix[meta_field_name_1]" value="<?= $value1 ?>">
    <input type="text" name="meta_prefix[meta_field_name_2]" value="<?= $value2 ?>">

    <input type="hidden" name="metabox_nonce" value="<?= wp_create_nonce(__FILE__); ?>" />
  <?php
}

add_action('save_post', 'saveMetaCallback', 0);

function saveMetaCallback($postId) {
  if (!isset($_POST['meta_prefix'])) return false;

  if (
    empty($_POST['meta_prefix'])
    || !wp_verify_nonce($_POST['metabox_nonce'], __FILE__)
    || wp_is_post_autosave($postId )
    || wp_is_post_revision($postId )
  ) return false;

  $fields = array_map(
    'sanitize_text_field',
    $_POST['meta_prefix']
  );

  foreach($fields as $key=>$value) {
    $fieldName = 'meta_prefix_'.$key;

    if(empty($value)){
      delete_post_meta($postId, $fieldName);
      continue;
    }

    update_post_meta($postId, $fieldName, $value);
  }
}