@VeryLongName 

Sorry for any confusion. I was focused on providing an alternative method of conveniently accessing the extender's management page, but should've provided more context.

If you can still access the management GUI after setting it up via www.tplinkrepeater.net, then the lender is operating as intended.

Once the extender joins your network, it will be given a dynamic IP address from your router's DHCP server. This is primarily why we suggest using the domain or Tether app post-setup since these methods can dynamically locate the extender.

However, if you are confident in locating the extender's new IP in your router's DHCP Client List—which may change as the router issues new DHCP addresses over time if their lease expires and renews—you might be able to access it using its new dynamic IP.

As for the login prompt at 192.168.0.254, is it possible that another device on your network has this IP address and prompts you for credentials when reached? Is it a different interface with any indication of another brand or model than your RE200? 

There is also the possibility that, in a network where the router's network schema doesn't follow a 192.168.0.x model, the 192.168.0.254 default IP will no longer be accessible once the extender joins the network since it is not within the schema.

I'll gladly pass along your operation manual feedback to the appropriate team. We also offer a wealth of FAQs and guides on our website to help users become more familiar with our products and their features, as well as common troubleshooting tips.