How to use Transparent Proxy and HTTPS traffic

You cannot use squid to access HTTPS with the transparent mode enabled.

What you could do is adding a rule to the firewall to enable the access to HTTPS.

Go to Firewall->Package Filter->Configure default rules, and in the rules section add a rule which contains the following: Protocol: tcp Port: 443 Destination: Action: Allow

Save changes. After that your users should be able to access HTTPS sites.