Hi!
​Can I see the result of ​ifconfig ​in Kali, ​ipconfig ​in the target machine, bettercap’s version, the command you used to start bettercap and the contents of the spoof caplet please?
Can you also show me Kali’s and Window’s network settings, so just right click the Kali machine from Virtual box >> Settings ?? Network, take a screenshot and post it here please.​​​

And you have to enable port forwarding using this command:
echo 1 > /proc/sys/net/ipv4/ip_forward

Don’t change the iptables rules cause that may interfere with internet connection.

Thanks!
Diego