Hi, To use any of the Amazon GameCircle services, you have to register your game in developer portal and include the Amazon GameCircle API. You can test non submitted GameCircle enabled apps in developer portal. Here's the general guidelines that can be followed incase you get CANNOT_AUTHORIZE error. 1) Test on a Kindle Fire device. Amazon GameCircle features are only available on Kindle Fire devices. 2) Make sure the device is signed in with an Amazon account. GameCircle uses the account that the device is signed in with to authenticate the player. 3) Make sure the device has been updated to the latest version of the Fire OS. To do this, go to the top menu, tap More, tap Device, click the Update your Kindle button if it is enabled. 4) Make sure you're using the latest version of the GameCircle API. The current version is 1.2.2. 5) Make sure that the keytool command you used to get the signature returned a valid result. To do this, run the first part of the command line separately: keytool -exportcert -alias androiddebugkey -keystore [path to your keystore file] This command should return a very long string that represents your certificate. If the path to your keystone is wrong, it will return an error message. After this you get valid results from this command, then run the full command line to get the signature: keytool -exportcert -alias androiddebugkey -keystore [path to your keystore file] | openssl sha1 -binary | openssl base64 This will return your signature string. Please check that this is the string that you have registered in the GameCircle Portal. Few links that may help you on this issue.