Install prerequisites. This will include:
-sudo apt install python3-gi gir1.2-gtk-3.0 gir1.2-webkit2-4.0 openconnect ocproxy
+ sudo apt install python3-gi gir1.2-gtk-3.0 gir1.2-webkit2-4.0 openconnect ocproxy
+
+Also, note that you'll need at least version 8 of openconnect. If you're not sure what you've got, run:
+
+ openconnect --version
2.