When importing – failed to import: Invalid post type feedback

I am attempting to import a site using XML generated by WordPress.com

All the posts and media seem to import, but the comments fail with errors

Failed to import “Sarah Toon - 2015-10-10 08:29:30”: Invalid post type feedback
Failed to import “Kylie - 2015-10-10 08:34:50”: Invalid post type feedback
Failed to import “Sophie Ward - 2015-10-10 08:36:22”: Invalid post type feedback

Reading other posts, here on WordPress.SE none of them have an accepted answer. The closest I could find is Custom post types not imported properly but that is about posts, not comments.

Can someone get me started on solving this please?

The issue is you’re trying to import posts with a post type of feedback, but there is no such post type registered on your install of WordPress.

Quick-and-easy fix is to register one:

add_action( 'init', function () {
    register_post_type( 'feedback', [
        'public' => true,
        'labels' => [
            'singular_name' => 'Feedback',
            'name'          => 'Feedback',
        ]
    ]);
});

Place it in your theme’s functions.php, or in a MU plugin (eg. wp-content/mu-plugins/feedback.php).