After setting up a VPN policy in to tunnel interface mode, ensure a route has been created on both sides to route traffic to the appropriate network. Then proceed to check access rules on the side of the tunnel which has the wireless network.
When creating route policies in which the source is any and traffic is set to pass to a non-trusted zone, the access rules are not auto-created.
The rules will need to be added in two places. From zone VPN to zone WLAN and from zone WLAN to zone VPN.
They will be similar to rules that are created from VPN to LAN and LAN to VPN where the VPN network is the remote network.