Extracting Woocommerce Custom Field or Product Attribute

I’m a Make newbee, working on my first scenario. In it’s current basic test form it is: Woocommerce > Iterator > Mail. I’ve set an extra field (Design ID) in Woocommerce. I’ve tried that both as custom field and as product attribute (with the standard WC options, no additional plugin). In Woocommerce itself this works fine. I can also access the custom field in other apps. But I can’t manage to extract it in Make, despite reading similar questions. In addition to this field, I have two other product attributes that I use for product variations (size and form). I have no problem extracting these.

I would expect the custom field or product attribute in Iine Items > Metadata. That is where I find the other product attributes. But I tried many other fields as well.

I’m missing something, but what?