If your Wavlink wn575a3 ac1200 WiFi repeater is blocked by the IPV6 firewall but to complete the wn575a3 ac1200 extender setup process, the first step would be disabling your router's firewall settings. This is because the IP version 6 settings on some routers tend to block the WPS pairing request from the repeater, which results in the repeater being unable to extend the WiFi range.

To disable the IPV6 firewall settings on your router, log in to the router web interface using the default login credentials. Go to the firewall settings section and look for an option to disable the IPV6 firewall. Once you disable it, save the changes and reboot the router. After disabling the IPV6 firewall, try pairing the Wavlink wn575a3 ac1200 WiFi repeater again. If it fails to connect to your network, try resetting the repeater to its default factory settings and pairing it again. If you've followed these steps and are still having trouble connecting the repeater, it is possible that your router may not support WPS pairing. In this case, you can manually connect the repeater to your network using a LAN cable. Simply connect the repeater to your PC or laptop using an Ethernet cable and access the repeater's web interface. You can then configure the settings manually to connect it to your network.

By following these steps, you should be able to fix the issue of your Wavlink wn575a3 ac1200 WiFi repeater being blocked by the IPV6 firewall and extend your WiFi range seamlessly.