Incorrect Wifi Password on N300 WiFi Range Extender Model EX2700

I followed the instruction to connect with WPS (my existed internet is Bell Modem White 4000), and all the lights (Power/WPS/Router) are solid green. And I also checked that there is excellent signal of my Ex2700. However, only when I input the same WiFi password that I use for my WiFi router, it doesn't work and says 'incorrect password'. What should I do? Please kindly advise. Thanks!