@sdetweil I tried with all options (http, https, webcal). The only thing that worked for me was backing up the config files, removing, and re-installing.

I am raspbian, just upgraded nodejs to 16.15.0 and receiving the exact same error.

edited to add: I tried the URL in a browser and it downloads the ICS file to my machine just fine. I also tried https and http, and using a public calendar as well.