`netsh interface ip set address "16" static xx.xx.xxx.xx 0.0.0.0 0.0.0.1 gwmetric=1 store=active` fails

As described in openconnect!306 (comment 744337009), vpnc-script-win.js script fails as follows on my Windows 10 (virtual) machine:

openconnect.exe --protocol=fortinet --no-dtls -u xxxxxxxx xxxxxxxxxxxxx.xxx.xx
GET https://xxxxxxxxxxxx.xxx.xx/
Connected to xxx.xxx.xxx.xx:443
SSL negotiation with xxxxxxxxxxxx.xxx.xx
Connected to HTTPS on xxxxxxxxxxxx.xxx.xx with ciphersuite (TLS1.3)-(ECDHE-SECP256R1)-(RSA-PSS-RSAE-SHA256)-(AES-256-GCM)
Password: POST https://xxxxxxxxxxxx.xxx.xx/remote/logincheck
GET https://xxxxxxxxxxxx.xxx.xx/remote/fortisslvpn_xml
Reported platform is FG22E1 v6.02.8 build 1232 branch 1232
Server reports that reconnect-after-drop is not allowed. OpenConnect will not
be able to reconnect if dead peer is detected. If reconnection DOES work,
please report to <openconnect-devel@lists.infradead.org>
Got IPv4 DNS server xxx.xxx.xxx.x
Got IPv4 DNS server xxx.xxx.xxx.x
Got Legacy IP address xx.xx.xxx.xx
Idle timeout is 25 minutes.
Requesting calculated MTU of 1351
Configured as xx.xx.xxx.xx, with SSL connected and DTLS disabled
Session authentication will expire at Fri Nov 26 10:17:40 2021

Microsoft (R) Windows Script Host Version 5.812
Copyright (C) Microsoft Corporation. Tous droits réservés.

Using Wintun device 'wintun', index 16
WARNING: Support for Wintun is experimental and may be unstable. If you
  encounter problems, install the TAP-Windows driver instead. See
  https://www.infradead.org/openconnect/building.html
Microsoft (R) Windows Script Host Version 5.812
Copyright (C) Microsoft Corporation. Tous droits réservés.

VPN Gateway: xxx.xxx.xxx.xx
Internal Address: xx.xx.xxx.xx
Internal Netmask: 0.0.0.0
Internal Gateway: 0.0.0.1
Interface: "wintun" / 16
MTU: 1351
Configuring "wintun" / 16 interface for Legacy IP...
"netsh interface ip set address "16" static xx.xx.xxx.xx 0.0.0.0 0.0.0.1 gwmetric=1 store=active" returned non-zero exit status: 1)
   stdout+stderr dump: ParamŠtre incorrect.



Script did not complete within 10 seconds.
Failed to spawn script 'c:\Program Files\OpenConnect\vpnc-script-win.js' for connect: L’opération a réussi.
Configured 2 DNS servers: xxx.xxx.xxx.x xxx.xxx.xxx.x
done.
Configuring Legacy IP networks:
Legacy IP route configuration done.