Calendar Invitation error - how to fix?

Hello Brosecarlsbad,

Thank you for using Apple Support Communities.

I understand that you are unable to respond to a calendar invitation, getting an error that "Your response to the invitation cannot be sent." Let's start with the following steps, try each one until you get a resolution to the issue:

1. On your iPhone, to to Settings > 'Your name' > iCloud. Turn off 'Calendars', wait a few minutes, turn it back on.
2. Update iOS on your iPhone. Update your iPhone, iPad, or iPod touch - Apple Support
3. On your iPhone, go to Settings > Passwords & Accounts. Select your account that is linked to your Calendar. Turn off Calendars. Turn your iPhone off and back on. Turn Calendars back on.
4. Force close the Calendar app and turn back on. How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support

If you still have the issues, get back with me and we can see where we need to go from there.

Best regards.