That usually happens when your Roku account somehow didn't get set up as a US account. I don't know of a reliable way to figure out what region it is associated with, but the only way to fix it is to start all over again. Factory reset the TV and create a new Roku account. Close the current account and make sure you clear your browser cookies, use a different browser, use a different device, or use a private/incognito browser window when you create the new account.
How to close your Roku® account | Official Roku Support
How to factory reset your Roku® streaming device | Official Roku Support
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