Auto-attach Images from Child Form to Parent Post

<?php
/**
 * Gravity Perks // Nested Forms // Auto-attach Images from Child Form to Parent Post
 * https://gravitywiz.com/documentation/gravity-forms-nested-forms/
 *
 * This snippet assumes you have a parent form that is used to generate to a new post via the Advanced Post Creation
 * add-on – and – a child form that contains a Post Image field. With this snippet in place, all images uploaded via
 * the child form will be automatically attached to the post generated for the parent form. Posts generated by the
 * child form will be deleted.
 */
// Update "123" to your parent form ID.
add_action( 'gform_advancedpostcreation_post_after_creation_123', function( $post_id, $feed, $entry, $form ) {

	$parent_entry  = new GPNF_Entry( $entry );
	$child_entries = $parent_entry->get_child_entries();

	foreach ( $child_entries as $child_entry ) {

		if ( ! $child_entry['post_id'] ) {
			return;
		}

		$attachments = get_posts( array(
			'post_type'      => 'attachment',
			'posts_per_page' => -1,
			'post_parent'    => $child_entry['post_id'],
		) );

		foreach ( $attachments as $attachment ) {
			wp_update_post( array(
				'ID'          => $attachment->ID,
				'post_parent' => $post_id,
			) );
		}

		wp_delete_post( $child_entry['post_id'] );

	}

}, 10, 5 );