You need to create a Marketing > Promotions of promotion type "Sales Order Detail" because here you're giving a discount when coupon is entered during checkout. In the promotion rule, choose from the Insert Template "10% discount with coupon free2".

Modify the rule, so it looks for your coupon name in lowercase "tryme" (because coupons are always converted to lowercase during checkout so that customer can use TryMe or tryme or TRYME and all will work). Then change discount calculation from -0.10 (for 10% discount) to -1.00 for (100% discount).

When the customer enters the coupon during checkout and click on review order, they will see a discount equivalent to the amount of the product that is given away for free.

Thanks again, I was using "Product" type promotion.

In case it helps anyone else when I first set this up it still didn't work. I had to create a new Coupon for some reason, but it worked perfectly with the new one.