Available apps are tied to the region associated with your Roku account. If you set up your Roku account when you weren't in the UK or while using a VPN or anything that could mask your true location your account won't be associated with the UK. It's also all too easy to create an account that gets associated with the wrong region through no fault of your own. The only way to fix it is to create a new account, factory reset your Roku device, and link it to the new account.
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