Connect Gravity Forms upload field to a Metabox image field

hdco_set_post_metabox_field.php

<?php

$gravity_form_id = 1; // gravity form id, or replace {$gravity_form_id} below with this number
add_filter( "gform_after_submission_{$gravity_form_id}", 'hdco_set_post_metabox_field', 10, 2 );
function hdco_set_post_metabox_field( $entry, $form ) { 
 $gf_images_field_id = 18; // the upload field id
 $metabox_field_id = 'images_gallery'; // the metabox field id
 
 if( isset( $entry['post_id'] ) ) {
    $post = get_post( $entry['post_id'] );
    if( is_null( $post ) )
        return;
    } else {
        return;
    }
 
    if( isset( $entry[ $gf_images_field_id ] ) ) {
        $images = stripslashes( $entry[ $gf_images_field_id ] );
        $images = json_decode( $images, true );
        if( !empty( $images ) && is_array( $images ) ) {
            $gallery = array();
            foreach( $images as $key => $value ) {
                if( function_exists( 'hdco_sideload_image' ) ) {
                    // Download the file in media library and get the Id
                    $image_id = hdco_sideload_image( $value, $post->ID );
                }
 
                if( $image_id ) {
                    $gallery[] = $image_id;
                }
            }
        }
    }

    if( ! empty( $gallery ) ) {
        foreach($gallery as $image_id) {
            add_post_meta($post->ID, $metabox_field_id, $image_id);
        }
        wp_update_post( $post );
    }
}

hdco_sideload_image.php

<?php

function hdco_sideload_image( $image_url, $parent_post_id = null ) {

    if ( !function_exists('media_handle_upload') ) {
        require_once(ABSPATH . "wp-admin" . '/includes/image.php');
        require_once(ABSPATH . "wp-admin" . '/includes/file.php');
        require_once(ABSPATH . "wp-admin" . '/includes/media.php');
    }
   
    if( empty( $image_url ) || ! esc_url( $image_url ) )
        return false;
    
    $image_url = esc_url( $image_url );

    $tmp = download_url( $image_url );
    if( is_wp_error( $tmp ) ){
        // download failed, handle error
    }

    $file_array = array();

    // File base name, e.g. image.jpg
    $file_base_name = basename( $image_url );

    $filetype = wp_check_filetype( $file_base_name, null );
    if( !empty( $filetype ) && is_array( $filetype ) ) {
        
        // Create attachment title - basically, pull out the text
        $post_title = preg_replace( '/\.[^.]+$/', '', $file_base_name );

        $file_array['name'] = $file_base_name;
        $file_array['tmp_name'] = $tmp;

        // If error storing temporarily, unlink
        if ( is_wp_error( $tmp ) ) {
            @unlink($file_array['tmp_name']);
            $file_array['tmp_name'] = '';
        }

        // do the validation and storage stuff
        $id = media_handle_sideload( $file_array, $parent_post_id);

        // If error storing permanently, unlink
        if ( is_wp_error($id) ) {
            @unlink($file_array['tmp_name']);
            return false;
        }

        return $id;
    } else {
        return false;
    }
}