You need to open the calendar event in Gmail to add your response. Notes from all guests are shown below their name in the guest list. Follow the steps below to learn how to add notes to new and existing events.
For new invitations1. Open the calendar event in Google Calendar.
2. Select your response at the top of the event. Add your note.
3. Click Save.
For events you have previously responded to1. Open the calendar event.
2. Click the Add a note or change your response link at the top of the screen.
3. Add your note and click Save.