Для решения этой проблемы вы можете воспользоваться этим кодом
add_action( 'gform_after_submission', 'set_post_content', 10, 2 );
function set_post_content( $entry, $form ) {
//if the Advanced Post Creation add-on is used, more than one post may be created for a form submission
//the post ids are stored as an array in the entry meta
$created_posts = gform_get_meta( $entry['id'], 'gravityformsadvancedpostcreation_post_id' );
foreach ( $created_posts as $post )
{
$post_id = $post['post_id'];
$post = get_post( $post_id );
require_once( ABSPATH . 'wp-admin/includes/image.php' );
require_once( ABSPATH . 'wp-admin/includes/file.php' );
require_once( ABSPATH . 'wp-admin/includes/media.php' );
$attach_id = media_handle_upload('file', $post_id);
if (is_numeric($attach_id)) {
update_option('option_image', $attach_id);
update_post_meta($post_id, '_my_file_upload', $attach_id);
}
update_post_meta($post_id, 'myname', $_POST['myname'];);
}
}