Thanks for reaching out. We're sorry to hear about the difficulties you're experiencing kindly email us a screenshot of your settings to firstname.lastname@example.org.
I too am trying to link ToDo with Siri on my iPhone 6 with IOS 11. I am following the instructions in this guide (http://support.appigo.com/support/solutions/articles/143954-creating-tasks-with-siri).
I get an error after trying to save the CalDAV settings headed "Calendar Account" with "CalDAV account verification failed". I have tried with SSL on and off and both don't work.
Please help! It must be a relatively simple solution.