the exec trick issue

hi.

yudeMacBook-Air:vpn-ws brite$ sudo ./vpn-ws-client --exec "ifconfig vpn-ws 192.168.10.2 netmask 255.255.255.0" vpn-ws wss://ws.smt.biz.st:449/ --no-verify
Password:
[Mon Sep 16 10:44:29 2019] vpn_ws_tuntap()/if_nametoindex(): Device not configured
yudeMacBook-Air:vpn-ws brite$ 

how to fix "Device not configured" issue?
tks 