Some iPhone users are getting reoccurring pop message saying “Calendar Invitation - Your response to the invitation cannot be sent - Ok”. Which is very annoying in itself as the pop is coming up in every 5 min. The issue is reported to last longer for like 2 months.
Below are some steps which can help to stop pop up on iPhone “Calendar Invitation. Your response to the invitation cannot be sent”
Fix 1: Turn off/on any calendar event
Recommend that try to turn any calendar accounts off and on again. To do this, open Settings > Calendar > Accounts. Choose any accounts here that you use your Calendar with and turn Calendar off and then on again.
Restart your iPhone before testing it again
Fix 2: Delete and add suspicious email exchange account
Delete any suspicious exchange email account and add them again.
When you add back email account after deletion you get everything back without any risk of losing calendar events.
Fix 3: Account specific re-add
Go to Settings>Accounts & Password
Select the account you believe is the problem
Turn off calendar (repeat w the other ones),
Turn off /start your phone
Turn your calendar/s back on
Now check again, problem should be fixed.