GoDaddy have a variable named isc. When you submit the coupon, GoDaddy will check in the database, if exists, they will send informations of the coupon to the check out page and you’ll get discounts corresponding the coupon has submitted.
But if don’t want lose the times, you can check before submit coupon code:
Hello, my name Dung Hoang, I'm a Webmaster. I usually purchase domain & hosting for my project, i using coupon/promo codes while ordering for save money. Now, i want share it to you.Connect me via: Google+ | Twitter | Facebook