Some Alexa devices require using our Monocle Gateway software running inside your network to facilitate the requirements for newer Amazon devices like the Echo Show 5 and all of the current generation FireTV 4K devices.
I don’t have a recent FireHD 8 to test with, but I suspect its the same issue.
More details here:
https://monoclecam.com/monocle-gateway
The information on this page outlines why this is needed. (albeit for the FireTV 4K – but same reasoning.)
https://forum.monoclecam.com/topic/112/fire-tv-stick-4k-3rd-generation-2018
Thanks, Robert