@A99999
Hi, did you configure the extender?
By default, the default wireless network of the extender is open, no password required, and after set up, it will share the same wireless password as the router, so please try to use your router wireless password to connect the extended network.
If it doesn't work, please reset the extender to factory defaults by holding reset button until all LEDs turn on momentarily, then set up the extender again from the beginning:
How to configure my RE200/RE210 via Web GUI to extend an existing wireless network’s coverage