Place an Order

Submits order placement.

POST/orders

Authorization

UDX-Access-KeyAPI key · headerrequired

Opaque API key ID.

UDX-Access-TimestampAPI key · headerrequired

Unix time in milliseconds, within 30 seconds of server time.

UDX-Access-SignatureAPI key · headerrequired

Standard-base64 RSA-PSS/SHA-256 signature with a 32-byte salt.

AuthorizationBearer token (JWT) · headerrequired

Bearer token for an active signed-in UDX user.

Header parameters

UDX-Versionstring

Dated API version (YYYY-MM-DD).

min length 10 · max length 10

UDX-Idempotency-Keystring

Optional client-generated key that makes a mutation safe to retry.

min length 1 · max length 255

Request body

requiredapplication/json

tickerTickerrequired

A human-meaningful natural key naming a single-leg or multi-leg market.

min length 1 · max length 128

client_order_idClientIdrequired

A client-supplied correlation identifier.

sideOrderSiderequired

Order side.

Allowed:buysell

quantityFixedPointQuantityrequired

A quantity in contracts as a fixed-point decimal string.

max length 24 · matches ^[0-9]+(\.[0-9]{1,2})?$

pricestringrequired

Limit price in YES price space, in dollars, regardless of side.

max length 24 · matches ^[0-9]+(\.[0-9]{1,6})?$

time_in_forceTimeInForcerequired

How long the order stays active.

Allowed:gtciocfokdaygtt

expires_atstring<date-time>

The instant a good-till-time order expires. Required when time_in_force is gtt and not accepted with any other time in force.

max length 40

post_onlyboolean

If true, the order only ever rests (adds liquidity); an order that would cross the book on placement is rejected. Incompatible with ioc/fok.

default: false

account_idstring

Account to place the order under. Required for an unrestricted API key; an account-restricted key uses its bound account.

min length 1

self_trade_prevention_typeSelfTradePreventionType

Which order gives way when an incoming order would match one of the caller's own resting orders.

Allowed:placedresting

Responses

202Order accepted for processing.

orderOrderSubmissionrequired

An accepted order submission.

Show properties

order_idEntityIdrequired

An exchange-assigned identifier. Treat it as an opaque, stable key with no internal structure.

min length 1

client_order_idClientIdrequired

A client-supplied correlation identifier.

400The request was malformed or the order was rejected at submission.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

401No valid credential was provided.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

403The credential lacks the trade scope.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

409This idempotency key is still in use, or its request completed with a response too large to replay. The problem type tells the two apart.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

422This idempotency key belongs to a different request.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

429The member rate limit was exceeded.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

500Something went wrong on UDX's side.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

503Either request admission is temporarily unavailable, or the submission itself failed indeterminately: the exchange may or may not have received the order.

typestring<uri-reference>required

A stable URN identifying the kind of problem, for example urn:udx:problem:insufficient-permissions. Branch on it rather than on the localized detail. It is an identifier, not a URL to dereference.

max length 2048

titlestringrequired

A localized, human-readable summary of the error category. Stable for a given status code and resolved language — clients must not use it as a machine-readable discriminator.

max length 40

statusintegerrequired

The HTTP status code, repeated from the response itself.

detailstring

A localized, human-readable explanation specific to this occurrence. Clients must not parse it for machine-readable information.

max length 500

instancestring<uri-reference>

An identifier for this specific occurrence, so it can be correlated with server-side logs if you need to report it.

max length 100

Request

curl -X POST "https://api.underdogexchange.com/orders" \
  -H "UDX-Access-Key: API_KEY_ID" \
  -H "UDX-Access-Timestamp: UNIX_MILLISECONDS" \
  -H "UDX-Access-Signature: BASE64_SIGNATURE" \
  -H "Content-Type: application/json" \
  -d '{
  "ticker": "UDX-EXAMPLE-MARKET",
  "client_order_id": "order-20260804-001",
  "side": "buy",
  "quantity": "100",
  "price": "0.55",
  "time_in_force": "gtc"
}'

Response

{
  "order": {
    "order_id": "BK9BZNTK8022",
    "client_order_id": "order-20260804-001"
  }
}

{
  "type": "urn:udx:problem:invalid-request-parameters",
  "title": "Bad Request",
  "status": 400,
  "detail": "invalid request parameters",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:order-rejected",
  "title": "Bad Request",
  "status": 400,
  "detail": "Order rejected; it was not placed",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:invalid-authentication-credentials",
  "title": "Unauthorized",
  "status": 401,
  "detail": "invalid authentication credentials",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:insufficient-permissions",
  "title": "Forbidden",
  "status": 403,
  "detail": "insufficient permissions",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:request-with-header-in-progress",
  "title": "Conflict",
  "status": 409,
  "detail": "a request with this UDX-Idempotency-Key is already in progress",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:response-too-large-to-replay",
  "title": "Conflict",
  "status": 409,
  "detail": "this request already executed, but its response was too large to replay; do not resend it with a fresh UDX-Idempotency-Key, read the affected resource to confirm the result",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:header-used-for-different-request",
  "title": "Unprocessable Entity",
  "status": 422,
  "detail": "UDX-Idempotency-Key was already used for a different request",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:member-rate-limit-exceeded",
  "title": "Too Many Requests",
  "status": 429,
  "detail": "this member has temporarily exceeded its request rate",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:order-outcome-unknown",
  "title": "Service Unavailable",
  "status": 503,
  "detail": "the order may or may not have been placed; check your orders before retrying",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}

{
  "type": "urn:udx:problem:request-admission-unavailable",
  "title": "Service Unavailable",
  "status": 503,
  "detail": "request admission is temporarily unavailable",
  "instance": "urn:request-id:8f14e45f-ceea-4abc-a743-e89a34d3f6ef"
}