Order receipt email content
This is not really an answer but closer to one than I've been before; even though I cannot go any further.

In /core/themes/bartik/templates I've placed a copy of commerce-order-receipt.html.twig. I can change the wording in this template, refresh the cache and I can see that come through in new emails. I see there's a mention of an 'order_entity' which I do not know how to reference so it appears in an email receipt.

If you can see the screenshot I've uploaded, it may become clear where I'm at or where I'm going wrong. 



I thought I might be able to change one of the columns in the order item (as the current four columns are exactly those that appear in receipt emails) and then try and reference it through {{ order_entity.getSomething }} in commerce-order-receipt.html.twig (after clearing the cache).

If I can get the fields in 'Purchased Entity' into the receipt email, I can then complete my business case for my Drupal site as everything else works a treat.

Thanks again.