As of Mar. 17, 2014 *ET, service will no longer be available for Kindle devices. It is possible to continue playing on your current account by performing a data transfer to an iOS or Andriod device, but please be informed that any unused Gold remaining in your account cannot be transferred to a device of a different OS.
Kindle Service Termination Schedule
Gold Shop Closing: Mar. 3, 2014 (Mon) 11:59pm *ET
Service Ending: Mar. 17, 2014 (Mon) 11:59pm *ET
*This schedule is subject to change.
A notification regarding any further changes will be posted in the application.
For further details regarding this matter, please follow the in-game Campaign Banner.