Just click this link and click the yellow “Get your $2 credit” button. Authorizing the app to post as your Twitter.
Amazon will tweet out the following message: Just got a $2 credit from @amazon_studios for movies + TV shows @amazonvideo. Click http://amazon.com/studios2u to get yours. #studios2u.
You have access to the credit immediately which is always good! When you order your video the credit is automatically applied.