Hi Assine, Thank you for posting. Application key must be set in order to get Mobile Ads working. If you create an app in Amazon Developer Portal, an unique key would be assigned to your app and you should use that in the code. Please note that if you create an app in the portal, it wont be published unless you submit your app to us after completion of development/QA and we complete our app verification process. If you need to integrate Amazon SDKs into your app you must be having your app defined in the developer portal. Please create one! Hope this helps.