How to add a product feature to supplier invoice?

I know there are some smart guys on this forum and hopefully one of you can help me.

I have set a product feature which I want to add to the supplier invoice email.

I have found the template for the supplier invoice email, supplier_invoice.tpl.

My question is, what code to I need to use in supplier_invoice.tpl to call a specific product feature, or even all product features?

I have tried using {$oi.product_features|default:“-”} and {$oi.feature.value|default:“-”} without success - unsurprisingly as I'm just guessing based on the existing code used to call the product code.

Can anybody point me in the right direction?

My goal is to include the supplier's own code (which I have set up as a product feature) in the supplier invoice, which is different from my own product code.

Thanks in advance!