Did the buyer say the code didn’t work? If not, don’t jump to conclusions. There are all kinds of buyers, some are conscious and rate the seller after they receive and use the code successfully. Others are oblivious or just don’t care. They get what they pay for and don’t rate you. It isn’t entirely their fault. Many of the selling sites that have been around for decades doesn’t require the buyer to rate the seller. Most of the time they pay and think you have the money already. The rating your seller method is still a fairly new concept. This is what the 3 day count down timer is for, so that you get automatically rated after 3 days. I know 3 days seems like a lot and from the thousands of sales I made, I’ve had my fair share of waiting for the 3 day auto-rating, but this is to ensure the buyer has a fair amount to time to make sure everything works and they don’t get scammed.
Another thing to keep in mind is to have good communication with your buyer. When I get a customer who has no ratings, it tells me they are new and likely doesn’t know how the rating process works. While you have their full attention before delivering the item, let them know that they should rate you after what they purchased is delivered and good to go. You can also put in your description for them to rate you after delivery. NEVER ask them to rate you in advance. That is fraudulent and will likely get you suspended. Hope this helps! Cheers!