And the WINNER is EMMA :)
Looks like the template I was using for the invoice style: "airy new" doesn't support this feature. When I change it to "bold" or "airy classic" it's working!
Thanks for everybody for the contribution.
So the solution is this: go to cog>select "custom form styles"> click "edit" on the template you want to modify>under "design" tab click on "change up template" > pick any but the "airy new" template.
