Originally Posted by
Evan!
When you return the car don't use the garage attendant. Return the car via the rental counter. You can give them the coupon code at that time (as well as confirm your DM# is in there as well).
I also went back onto the Avis website and clicked the Add Frequent Flyer Account on my reservation page (after the fact) and the miles and bonus posted today, and just waiting now for the 50% bonus sometime this week.