You cannot enter a network IP for gateway IP

Hi and Welcome to Sophos Community,

Gateway IP must be a specific IP address, it can never be technically correct to define a network address in this field.

Thanks

As Aditya Patel said,

the gateway IP address must in the WAN IP subnet range.

If you assign an out of range IP on gateway, it will show the alert to warn you.

You're right: gateway is not in the host's range. Thanks for confirmation.

You're right: gateway is not in the host's range. Thanks for confirmation.