Help & troubleshooting for network issues, including connecting your device to your home Wi-Fi network, connecting to public networks, troubleshooting wireless issues & ethernet connections, and optimizing streaming performance.
Is this happening on initial setup, or was it working before and now is not?
Two possible issues:
Your Express is a budget model that has a single band wifi receiver. It can connect to the 2.4 GHz wifi band but not the 5 GHz band. Make sure your wifi router is not 5 GHz only, or if it is a dual band, make sure the 2.4 GHz band is enabled.
I have had problems on occasion where my various Roku models stopped seeing my local wifi network exists, even when other devices in the house have no trouble connecting. I've been able to solve this by restarting the router. After the router comes back up, if the problem has not been corrected, restart the Roku (Settings > System > System restart) to start with a clean slate and try to reconnect. This makes no sense to me and I don't understand why it would work, but it has worked for me.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T