Do you have WiFi? Do you connect other devices to WiFi already? Your phone, for example?
You said you have a Roku Express 4K. That has been discontinued in the USA. The Roku Express 4K+ is the current version of that line. It's a different device, with different WiFi support. I'm not sure where you are, as you didn't share that information. If you're in the USA, then you bought an old device. Still, perhaps we can help.
If you're outside the USA, it depends on where you are, as WiFi standards are not universal. Some WiFi channels used in other countries aren't supported by Roku, if those channels aren't available in the US.
So, which device do you have? The model number is important. I know what you said you have, but the model number will still be helpful in confirming what you have.
Which band is your WiFi using? 2.4 GHz or 5 GHz? Or both? And what channel(s) is your WiFi network using?
DBDukes Roku Community Streaming Expert Note: I am not a Roku employee.
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