Wordpress snippet to get all categories except the first level

wp_get_categories_from_2_level.php

$args = [
  'taxonomy' => 'product', // Taxonomy type
  'hide_empty' => false, // Display all categories including empty ones too
  'exclude' => 15 // ID of default, uncategorized category or any taxonomy (optional)
];
$topLevelCategories = get_categories($args); // Query to get all categories

$childCategories = getChildCategories($topLevelCategories);

function getChildCategories($categories) {
  $childCategories = [];
  foreach ($categories as $category) {
    if ($category->parent != 0) {
      $childCategories[] = $category;
    }
  }
  return $childCategories;
}