After Thursday 3/31, the Amazon appstore will no longer allow updates to be submitted with minSdkVersion < 25.

Effectively, this is a software updates EOL for Fire OS 5 devices, meaning if you're supporting these devices, they'll be permanently stuck with whatever version you have as released on that date. Devices affected are original Fire TV devices, tablets, etc.

Link: https://developer.amazon.com/docs/app-submission/device-filtering-and-compatibility.html#minimum-api-levels-for-targetsdkversion