Extender AC750 Model EX3700

I have recently changed broadband router. I have connected the EX3700 range extended via WPS and the green light is on. In my list of wifi connections, the router name is shown and has the 2GEXT and 5GEXT options as available, so all looks good.

However, when I try to connect a device to those networks, the password for the router doesn't work. Yet when I connect a device to the router directly, the password is fine.

so it seems there is an issue with the passord connecting through the wireless extender, which doesn't make sense as the same password should work.

Also, I cannot connect to the extender as I can't access it due to not being able to connect a device to its signal.

Does anyone have any advice or solutions?

Thanks