Reminders - Can't share list

Everything is on with both my wife's phone and mine. iCloud is on and Reminders icloud is active> the list is in a 'shared' state whatever that means, but not "with" anyone. Whenever I try too add someone via text, I get an error in the sms app that says Collaboration Not Available - Unable to start collaboration.

FWIW, I have iMessage off, but that shouldn't matter. I've tried sending links also and the error for her is that the list is either not shared any more or she doesn't have permission to view it.

I've verified that she and I both are using a gmail acct for iCloud, and not our phone numbers.

Thanks