Try entering Pi-hole's IPv4 twice.
If that doesn't work, try 0.0.0.0 as second.
If that is rejected as well, put in an unused(!) IP from your router's reserve, i.e. outside of your router's DHCP pool range.
Try entering Pi-hole's IPv4 twice.
If that doesn't work, try 0.0.0.0 as second.
If that is rejected as well, put in an unused(!) IP from your router's reserve, i.e. outside of your router's DHCP pool range.