Status Codes and Error Responses

Either when an error occurs or when a response is successful, the response header contains an HTTP code, and the response body usually contains:

The HTTP response code
The message accompanying the HTTP response code
The field or object where the error occurred (if the response returns information about an error)

HTTP response code	Description
200	“OK” success code, for GET or HEAD request.
201	“Created” success code, for POST request.
204	“No Content” success code, for DELETE request.
300	The value returned when an external ID exists in more than one record. The response body contains the list of matching records.
400	The request couldn’t be understood, usually because the JSON or XML body contains an error.
401	The session ID or OAuth token used has expired or is invalid. The response body contains the `message` and `errorCode`.
403	The request has been refused. Verify that the logged-in user has appropriate permissions.
404	The requested resource couldn’t be found. Check the URI for errors, and verify that there are no sharing issues.
405	The method specified in the Request-Line isn’t allowed for the resource specified in the URI.
415	The entity in the request is in a format that’s not supported by the specified method.
500	An error has occurred within Force.com, so the request couldn’t be completed. Contact salesforce.com Customer Support.

Incorrect ID example

Using a non-existent ID in a request using JSON or XML (request_body.json or request_body.xml)

{
  "fields" : [ "Id" ],
  "message" : "Account ID: id value of incorrect type: 001900K0001pPuOAAU",
  "errorCode" : "MALFORMED_ID"
}

Resource does not exist

Requesting a resource that doesn’t exist, for example, if you try to create a record using a misspelled object name

{
  "message" : "The requested resource does not exist",
  "errorCode" : "NOT_FOUND"
}