Unfortunately AZ have been much more cautious with their coupons recently than in the past.

To get your coupon to work, I think you have to go onto the local Alitalia website of your departure country and see what coupon is advertised there. Then check that your flight doesn't go against any of the restrictions (eg there's a black out period around end October/early November), and finally the coupon should work (again, only on the local website of your departure country). If your country doesn't have a dedicated website, then check if there's a general code available on www.alitalia.com/EN_EN

I've received several e-mails about similar promotions over the past weeks. Basically it's worth checking for a discount code if you're planning to book an AZ ticket for an off-peak period. Discount codes for peak periods on the other hand have been very rare over the past six months.