Error responses

#HTTP status codes

Code	Meaning
`200`	Success
`201`	Resource created
`400`	Request body / query validation failed
`404`	Resource does not exist
`429`	Rate limit exceeded
`500`	Server error

#Response envelope

{
  "statusCode": 400,
  "error": "Bad Request",
  "message": [
    "outcomeId must be a string",
    "side must be one of: BUY, SELL"
  ]
}

Field	Description
`statusCode`	The same number as the HTTP status
`error`	A short human-readable label (`"Bad Request"`, `"Not Found"`)
`message`	string or string[]. Validation failures are always an array.

message can be an array

Validation failures from the NestJS ValidationPipe always come as message: string[]. Don't just show error.message as a single line — render each element of the array separately.

#A pattern for handling it on the client

type ApiError = {
  statusCode: number;
  error: string;
  message: string | string[];
};
 
async function call() {
  const res = await fetch(url, init);
  if (!res.ok) {
    const err = (await res.json()) as ApiError;
    const messages = Array.isArray(err.message) ? err.message : [err.message];
    throw new Error(messages.join('\n'));
  }
  return res.json();
}

#Common scenarios

Situation	Response
`outcomeId` missing	400 + `["outcomeId should not be empty"]`
Invalid enum	400 + `["status must be one of: ACTIVE, ..."]`
Market not found	404 + `"Market not found"`
Rate limit	429 + `"ThrottlerException: Too Many Requests"`

#Rate limit

Public endpoints are rate-limited per IP at the application level — see Rate limits for the current numbers.

If you get a 429, retry after a short backoff (a few seconds). If you're persistently blocked, consult the Retry-After header.

#Next

Pagination — the list envelope on successful responses
REST → Markets — the actual endpoints

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