Google Calendar API event insert always return 404 "not found" error

To JuanPablo, Re non-primary calendar:

In case of non-primary calendar you have to use the id (in form of an email address) as the calendarId.

Example: Let's say you have a calendar named 'test'. You get its id like this

GET https://www.googleapis.com/calendar/v3/users/me/calendarList?key={YOUR_API_KEY}
->
{
 "kind": "calendar#calendarList",
...
 "items": [
  {

   "kind": "calendar#calendarListEntry",
   "etag": ...,
   "id": "[email protected]",
   "summary": "test",
   "description": "Testing calendar for development of Calendar related applications",
...
   }
  }
 ]
}

Your POST will then look like this

POST https://www.googleapis.com/calendar/v3/calendars/[email protected]/events?sendNotifications=false&fields=start&key={YOUR_API_KEY}

I believe it's telling you that the calendar "test" resource cannot be found. Have you created a calendar called "test"? If you replace "test" with "primary" (your main calendar) then the Explorer should work.