How to add event .ics attachment to calendar on iPhone

I recently signed up for an online event and received an email with an .ics attachment. After various unsuccessful attempts to add, export/import, "open in..." etc. I discovered that I was overthinking it. Instead of using the .ics file directly, I opened the native Calendar app and clicked on "Inbox" at the bottom of the screen. I saw a list of invitations, found the one I wanted to add, and clicked on Accept. If you don't see the invitation, you may want to click on the "Replied" tab.. The event appeared in my calendar. This feels awkward - I'd rather not have to leave my inbox, but seems to work for me. Did not see this solution in previous posts above. Hope this helps someone.