Inserting Coupon code field

[permaculturegeek]

Hopefully my last question for this event!

I have created a Discount of 100% so that organisers and volunteers can register and we can have all participant details in one place. But I can't see how to insert a coupon field in the registration pages.
Ideally it should apply per participant, but if it can only work per booking, all good - we'll just tell people the codes are sent to to book separately if they are bringing paying family members.

I have attached the discount to the event and left all the automatically apply fields blank - it has a randomly generated code with a finite number of uses.