I finally figured out my firewall on my pihole device (old laptop running mint) was blocking my clients. When I turn off the firewall pihole works as expected. I tried denying all incoming and just allowing port 53 as that was the port for pihole-FLD. that does not work. However there were several other ports for some other applications that I do not recognize such as lighttpd, avahi-daemon etc. that were indicated in the firewall report.
Should I open those as well?
I would rather not leave the firewall off even though my pihole is behind a router that is behind a router.
If your laptop running Mint is inside your home network, it doesn't need a firewall running if is only running Pi-Hole. None of the laptop ports are open to the internet because it's behind your router. When Pi-Hole is installed on a Pi, there is no firewall on the Pi.
If you must have your laptop with a firewall, you will need to open the ports described in the link (check your debug log for the specifics for your installation as you may have additional software installed).
OK thx much - yep only running pihole on the laptop behind two routers but I allowed the ports shown in the debug log anyway and all else is denied and pihole is running fine so I will leave it. Although I get it that it is not really required.