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All Events endpoints return a consistent error shape:
{
  "error": "VALIDATION_FAILED",
  "details": [
    {
      "reason": "REQUIRED",
      "field": "userId",
      "message": "userId is required"
    }
  ]
}

HTTP status codes

HTTP StatusMeaning
200Success — event or request accepted
400Bad request — invalid JSON or failed validation
401Unauthorized — missing or invalid API key
404Not found — user identifier not found (Track API / Customers only)
503Service unavailable — auth cache temporarily unavailable
500Internal error — unexpected failure

Fields

FieldTypeDescription
errorstringMachine-readable error code
detailsarrayOptional list of field-level validation problems
details[].reasonstringWhy the field failed (for example REQUIRED)
details[].fieldstringField name that failed validation
details[].messagestringHuman-readable explanation
For authentication failures, see Events Authentication.