Display the reduction amount for a product in an invoice

[Cypher-key]

Hi, it's me again, and I'm -again- seeking your help.
Maybe it's just an oversight on my end, but I did not seem to find how you can display the reduction amount for a product on an invoice if the product have a reduction for a website on prestashop 1.7.7.2.
For the record, reduction_percent displays teh percentage, but reduction_amount, reduction_amount_tax_incl and reduction_amount_tax_excl display nothing.

Does anyone have a solution?

Thank you in advance!