Here Apple making it clear that they don’t want anything that looks spammy inside their app store. Apple has changed their review system with the new one doesn’t allow one to write a review for the app if it’s redeemed using a promo code.
According to Apple the change is mainly to stop developers who are using the codes to boost up their app and profile. There is lots of review exchange processes running around where all carried out by using the promo codes. Here is one response from the Apple support which reveals the latest update.
Anand here again from iTunes Store Customer Support. Thanks for writing back and letting me know your concern. I understand that you are still not able to write a review. I know how disappointing it can be when things don’t work out the way they should. I am sorry to inform that it is no longer possible to rate or review an app if it was downloaded using a developer’s promotional code.
However, I took the liberty of submitting your feedback to Apple on your behalf. Please know that Apple takes the feedback from our customers very seriously. This is the reason for our feedback page – to create a forum where our users can vent, praise or share whatever feelings they have to allow us to meet your needs, and grow as a company. I suggest that you use the link in order to share your feedback with us. I would also encourage you to share this link with all of your friends and family who wish to submit the feedback, and have them all submit the same request.