EX 7500 Set-up/Security Question

Trying to perform the initial set-up of my EX7500 extender. I have Century Link internet and use a Zyxel C3000Z modem/router combo.

The EX7500 instructions state "If your router's wifi security is set to WPA or WPA2 enterprise, your extender can't connect to your router. You must change your router's wifi security setting".

Going into my modem/router settings menu, there is no other wireless security setting available besides WPA or WPA2.

Is there any way to get this extender to work with my modem/router or do I need to find a different extender?

Thanks!