ipad: Cannot verify server identity

I get a popup on my ipad every so often "Cannot verify server identity, The identity of ics.ecal.com cannot be verified".

Since this seems to refer to calendars, I checked my calendars (both google and apple) and all calendars are functioning calendars that I set up, with one exception which I've deleted (unsubscribed and removed through google). I'm still getting the message after this.

Other posts here have issues with mail accounts, but that doesn't seem relevant to a calendar issue.

8th gen iPad, ios 16.5

How to fix or what other information can I provide?