I just updated the Drupal Commerce installation to beta 7 which includes support for promotions and coupons. I just can't seem to get the coupon redemption form in the cart to test this functionality. I checked the cart view, there is a field 'Coupon' in the global footer, but that is just meant to show the already activated coupons I believe. At least it didn't do anything for me.
I tried to add 'Coupon' to my relationships in the view, but this broke down the website (incorrect query generated).
In the code I also noticed the CouponRedemption FormElement. I'm not sure how to add this to my cart (view), but that seems to be what I need.