I am trying to set up/access the AC1200 (EX6110) wifi range extender for the first time.

My router is the AC1900 Nighthawk WiFi Range Extender Model EX7000. and it does not have an WPS button so I need to login wirelessly to the extender to begin the set process (as no ethernet port on extender). The issue seems to arise when I select the extenders network that I need a password..... there is no separate password issued with the device so I assume I am supposed to enter my router password. The router password is not accepted by the extender and thus I cannot progress with the installation.