In September I bought something using the BB Android App and it asked me at checkout if I wanted to apply my 10% birthday coupon. Did you try from the iOS or Android app?
The email I got had a link to click to get the deal. I assume if you did that and then put the game in your cart it should probably also work.
I tried the app yeah. I honestly might just be a total moron here. I don't see any area to apply the discount either on desktop or mobile. There's an area where it should be, it says My Best Buy Rewards and Offers. This is considered an "offer" in my account but that area is empty. It's not a big deal, like I said it's $1.50. But I wouldn't be on this site if I didn't strive to save every cent as a matter of principle.
I'll just buy it, and when I pick it up show the offer. If they can add it, cool. If not, oh well.