@Topiltzin80 The local admin password should be the same in AP mode. You can try setting a simpler password and check if this is the culprit.

@SteveF161 To rule out signal strength issue, you could connect the RE315 in the same room where your main router is. Test if the RE315 is working as expected and then you can relocate it at position...

@MikeSay You can name the SSIDs the same or different - it's your choice. It's up to your devices (mobiles, laptop, etc.) to decide when they will roam between the router and the RE.

@Kortezzee Double-check your wireless password. If the issue persists use a simpler password. Here's a guide on characters you have to consider when choosing a wireless password.

@jhafranco From its tech specs: 6× Fixed High-Performance Antennas

@SianLockwood Does the extended network use the same name as the host netwrok or different ? Do you receive any error message while trying to connect to the extended network ?