Can't import a file

[danielrcollins1]

I'm trying to use Calendar Import-Export on a Moto G6 Play device, running Android 9, without any attached Google accounts. Under Settings > Compatibility, I have all the permissive settings checked on. As a test I've downloaded a schedule from Tabletop.events (gaming convention registration site) as a file "tickets.ics".

On attempted import with Calendar Import-Export,I get the error: "Error at line 1:Expected [BEGIN], read [BEGIN]". Any ideas? What other info would be helpful?