Hello @Nicolas_di_Rago ,
Thanks for posting. Amazon Appstore has discontinued the Creator Service and the web-based app submission process for all devices, including Fire TV. If you previously used these services to create apps for Fire TV or tablets, you can update your apps to a new version in Amazon Developer Console.
All apps have been converted to Android apps on Amazon Developer Console. You can update your apps by submitting a new Android package app, with the same package name and a higher version number.
For more information please see the document: