Display post thumbnail of relationship

What am I doing wrong, can't get the relationship post thumbnail to display.

Sorry for this probably dumb question but stuck at the moment

{% set args = {post_type: 'radiator', nopaging: true, relationship: {id: 'radiator-project', from: post.ID}} %}
{% set products = mb.get_posts( args ) %}

{% for product in products %}
    {{ mb.get_the_post_thumbnail( product.ID, 'thumbnail') }}
    <a href="{{mb.the_permalink(product.ID) }}">{{ product.post_title }}</a>
{% endfor %}