iCloud Calendar private sharing invitations not sending

My iCloud Calendar can’t send any sharing invitations.

I’ve tested with multiple email addresses (including my own Gmail), on Mac, iPhone, and iCloud.com.

The share dialog says it sent, but no email ever arrives.

Public link sharing works, but private ‘Share With’ invitations don’t.

I created a brand-new iCloud calendar and it still can’t send invites.

I’ve already tried signing out of iCloud and toggling Calendar off/on.

Can you please reset calendar sharing / my iCloud calendar server for this Apple ID?