See @mgrant post extract below from the following thread on Radicale.
https://forum.emclient.com/t/caldav-and-carddav-setup/95911/2
I figured this out. I was using the incorrect URL. The URLs for Radicale look something like this:
https://myhost.com/radicale/myusername/12345678-1234-1234-1234-1234567890ab/
I had to create this by going to https://myhost.com/radicale/ and log in to the webpage. I had to create separate calendar and contacts and add 2 separate accounts.