You don't even need Amazon Underground on your device. just click Get App on one of the FREE apps, save on your cloud, and you'll get $5.
Note:
As a purchaser of select apps or games from Amazon Underground you have earned a $5 promotional credit to your account. This credit will be automatically applied to your next purchase of any eligible item sold and shipped by Amazon.com and is valid through February 26, 2016.
http://www.amazon.com/b/ref=as_li_ss_tl?_encoding=UTF8&camp=1789&creative=390957&linkCode=ur2&linkId=dfd4d56d73402dd9f0eb96e15f634421&node=13548855011&tag=mysa09-20&
linkId=4OS7PJY2PAXQN64X
Note:
As a purchaser of select apps or games from Amazon Underground you have earned a $5 promotional credit to your account. This credit will be automatically applied to your next purchase of any eligible item sold and shipped by Amazon.com and is valid through February 26, 2016.
http://www.amazon.com/b/ref=as_li_ss_tl?_encoding=UTF8&camp=1789&creative=390957&linkCode=ur2&linkId=dfd4d56d73402dd9f0eb96e15f634421&node=13548855011&tag=mysa09-20&
linkId=4OS7PJY2PAXQN64X