Hello Sangaris
Thanks for posting in the Roku Community!
For your Express or Roku Premiere device, please note that this is only compatible with wireless b/g/n networks on the 2.4 GHz network. In order for the device to connect, confirm that your router is broadcasting a 2.4GHz Wi-Fi network. You can check your device model by navigating to Settings > System > About.
If you are getting an error code or message, refer to this link for common Roku error codes and their recommended actions: How to connect your Roku® streaming device to the internet using Wi-Fi® or Ethernet
Let us know how it goes!
Regards,
Karla