AC1900 can't connect to TP-Link Archer A6 router

My extender worked fine with my previous ISP-provided router. I've used both the wizard and WPS but the result has been the same. When I use WPS, the TP-Link management tool says the client was added successfully. But if I connect to the extender, the genie app says it couldn't connect and check the passkey (which is correct). I've messed with a few settings on the router with no luck. I've also checked the system log which only contains the WPS events (successful).

Is there any diagnostic information available from the extender?

Appreciate any assistance!