wp_insert_post and blank page

I’m trying to process a form and the page should forward to header('Location: https://www.test.co.uk/thankyou');. I’ve turned on WP_DEBUG and the page is still blank. I’ve read that it may be a fatal error. This is my full page.

<?php
$art_title = $_POST['art_title'];

$i = 0;
foreach($art_title as $value) {
$art_title = $_POST['art_title'][$i];
$art_width = $_POST['art_width'][$i];
$art_height = $_POST['art_height'][$i];
$art_price = $_POST['art_price'][$i];
$art_creation_date = $_POST['art_creation_date'][$i];
$art_upload = $_FILES['art_upload'][$i];

	 $post = array(
      'post_content'   => '', // The full text of the post.
      'post_name'      => $art_title, // The name (slug) for your post
      'post_title'     => $art_title, // The title of your post.
      'post_status'    => 'draft', // Default 'draft'.
      'post_type'      => 'product', // Default 'post'.
      'post_author'    => '', // The user ID number of the author. Default is the current user ID.
      'menu_order'     => '0', // If new post is a page, sets the order in which it should appear in supported menus. Default 0.
      'post_password'  => '', // Password for post, if any. Default empty string.
      'post_excerpt'   => '', // For all your post excerpt needs.
      'comment_status' => 'open' , // Default is the option 'default_comment_status', or 'closed'.
      'post_category'  => '' // Default empty.
    );
    $post_id = wp_insert_post( $post);
    wp_set_post_categories( $post_id);
    add_post_meta($post_id, '_width', $art_width, true);
	add_post_meta($post_id, '_height', $art_height, true);

    $filename = $_FILES["art_upload"][[$i]["name"];
    $uploads = wp_upload_dir();

    //file_put_contents($file, $image_data);
    $file_array = array(
            'name'          => $_FILES['art_upload'][$i]['name'],
            'type'          => $_FILES['art_upload'][$i]['type'],
            'tmp_name'      => $_FILES['art_upload'][$i]['tmp_name'],
            'error'         => $_FILES['art_upload'][$i]['error'],
            'size'          => $_FILES['art_upload'][$i]['size']
    );

    // required for wp_handle_upload() to upload the file
    $upload_overrides = array( 'test_form' => FALSE );

    if ( !empty( $file_array['name'] ) ) {
       // upload the file to the server
        $uploaded_file = wp_handle_upload( $file_array, $upload_overrides );

            // checks the file type and stores in in a variable
        $wp_filetype = wp_check_filetype( basename( $uploaded_file['art_upload'] ), null );
           // set up the array of arguments for "wp_insert_post();"
        $attachment = array(

            'post_mime_type' => $wp_filetype['type'],
            'post_title' => preg_replace('/.[^.]+$/', '', basename( $uploaded_file['art_upload'] ) ),
            'post_content' => '',
            'post_author' => '',
            'post_status' => 'inherit',
            'post_type' => 'attachment',
            'guid' => $uploads['url'] . '/' . $file_array['name']
        );

        // insert the attachment post type and get the ID
        $attach_id = wp_insert_attachment( $attachment, $filename, $post_id );
        $attach_data = wp_generate_attachment_metadata( $attach_id, $uploaded_file['art_upload'] );
        require_once(ABSPATH . 'wp-admin/includes/image.php');
        // update the attachment metadata
        wp_update_attachment_metadata( $attach_id,  $attach_data );
        $post_thumbnail_id = get_post_thumbnail_id( $post_id );
        set_post_thumbnail( $post_id, $post_thumbnail_id );
    }

$i++;
}

header('Location: https://www.test.co.uk/thankyou');
?>

What do i need to add to this code to get it working? require code?