Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
Maybe Prime is not available in Saudi Arabia? Just because you are using a US account does not mean you can use a channel anywhere. You can only use channels authorized in the country the Roku is being used in.
Prime might be available there, but that doesn't mean that Amazon has approved it for Roku devices there. Roku themselves have no control over what geographical locations channels are available. It's under the total control of the channel developers, in this case Amazon. And if you contact Amazon and ask, unfortunately you'll likely get stuck with them saying it's available, because they don't understand the difference between service availability and device availability. You just have to keep bugging them to authorize their channel in the Roku channel store for your location.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.