Each of the product have a Toolset custom field value. That value is a PDF uploaded via custom field. We need this link to be accessible directly from order email confirmation.
I tried this kind of stuff (and a lot of other combinations 🙂 in email-order-items.php and functions.php
I suspect the problem is as simple as Types custom fields are stored with a prefix of 'wpcf-', so if the slug of your custom field is 'my-custom-field' then the key in wp_postmeta is actually 'wpcf-my-custom-field', which is what you should use in your get_post_meta call.