@Jader31 While Roku devices are supported in Brazil, it's up to the service provider (in this case Amazon) to determine if their service is available in a specific country. It is immaterial that it's available on your Samsung TV, as it's a completely different platform and uses a different programming language. Amazon has to make Prime Video available in a specific country, and Roku cannot alter the settings that Amazon configures for their app.
Roku cannot control what a 3rd party does with their app, so you need to ask Amazon why they don't permit their app to be available in Brazil when it appears obvious that they offer their service in that country. Unfortunately, I can also see the Amazon support person telling you their service is available, and not listen to the issue that it's not available on Roku devices.
One other possibility: if your Roku user account was created in the US before you moved to Brazil, that too could be a problem. Your user account country must match your actual location for the channel store to confirm your eligibility for installing certain apps. Since you mention that it's visible but not available to install, that might be the problem. Your only solution is to create a new user account while you're there in Brazil. Roku cannot change the country of your account, so you need a new one. You would then need to do a factory reset on your Roku and set it up using the new user account.
Just a caution, Roku does not permit discussing the use of a VPN here, as it's a method of bypassing legal restrictions on content in other locations. So further discussion about it could have your posts removed.
Dan
Roku Community Streaming Expert
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