Verified games have access to several awesome features, reward codes integration is one of them. This feature allows you to upload a series of bonus codes and control the way they are distributed to the players. This will give additional motivation to people to write you reviews, and helps reward the loyal players. Giving out codes is also great to promote special events in your game and celebrate things.
From the reward codes interface you can see at any time how many codes you have available, decide how many to give maximum for same user and if to give them out for any vote or just for written reviews, its up to you!
We recommand to upload at least 100 codes, regardless of their value (1 cent is fine too). You could also use them as tombola tickets inside your game and organize an extraction every month for the winning code.
The verification of your game is totally free but requires your attention quite a bit. It is a process to determine if you are indeed owner of the listed game or not and if you are maintaining the page yourself or its just a fan site maintained by a player. This is not a paid feature. Check out this page for more details on how to validate your game and enjoy these extra features.