iPhone can't verify CalDAV account
The answers provided helped me resolve my CardDAV verification issue.  Here are the exact steps I took:


Sign in to your Google Account at:   https://myaccount.google.com/
In the Sign-in &amp; Security section select:  ‘Signing in to Google’
Select ‘App Passwords’
From the dropdowns:  Select the app (contacts) and the device (iphone)
Follow the instructions in the pop-up to enter the verification code as the password for your google account on your phone.


I have IOS 11.4.