Reference

Error codes

Rejection codes in decisions and HTTP error codes from the services.

A2M reports failures in two places:

In a signed decision. A rule that fails produces a REJECT decision whose code and message name the rule. This is a normal, attributable answer, not a transport error. Over MCP it is returned as a tool result the model can read.
As an HTTP error. Malformed requests, conflicts, executor refusals and outages return an HTTP status and a body:

{ "error": { "code": "A2M_BAD_SIGNATURE", "apex_code": null, "category": "validation", "message": "decision signature did not verify" } }

category is validation or operational. apex_code is an optional secondary code aligned with the error classes of the draft APEX agent-venue specification, where one applies. A 4xx other than 408 and 429 will not succeed on retry.

Rule rejections (in decisions)

Code	Secondary	Meaning
`A2M_AGENT_UNKNOWN`	`APEX_4002`	Agent is not registered
`A2M_AGENT_REVOKED`	`APEX_4002`	Agent is revoked
`A2M_MANDATE_INACTIVE`	`APEX_4002`	Mandate is missing, revoked or expired
`A2M_MANDATE_AMBIGUOUS`	`APEX_4002`	More than one live mandate; fail closed
`A2M_INSTRUMENT`	`APEX_4010`	Instrument not on the mandate allowlist
`A2M_VENUE`	`APEX_4011`	Venue not on the mandate allowlist
`A2M_INSTRUMENT_UNKNOWN`	`APEX_4010`	Instrument not listed on the venue
`A2M_INSTRUMENT_HALTED`	`APEX_4030`	Instrument is halted or not tradable
`A2M_UNSUPPORTED_PRODUCT`	`APEX_4010`	Product class has no risk treatment yet; fail closed
`A2M_UNIT_INACTIVE`	`APEX_4011`	No active protected unit for this venue and product
`A2M_ORDER_TYPE`	`APEX_4011`	Broker does not accept this order type
`A2M_TIME_IN_FORCE`	`APEX_4011`	Broker does not accept this time in force
`A2M_ACCOUNT_UNKNOWN`	`APEX_4002`	User has no account at the venue
`A2M_ACCOUNT_INACTIVE`	`APEX_4002`	Account is not active
`A2M_MARKET_CLOSED`	`APEX_4030`	Instrument session is closed
`A2M_STALE_PRICE`	`APEX_4024`	Reference price missing, invalid, stale or in the future
`A2M_LOT_SIZE`	`APEX_4011`	Quantity is not a whole number of lots
`A2M_TICK_SIZE`	`APEX_4011`	Limit price is not on the tick
`A2M_PRICE_BAND`	`APEX_4011`	Limit is outside the market price band
`A2M_PRICE_COLLAR`	`APEX_4011`	Limit missing or outside the mandate price collar
`A2M_BROKER_NOTIONAL`	`APEX_4011`	Notional below the broker minimum or above the maximum
`A2M_FAT_FINGER_QTY`	`APEX_4011`	Quantity not positive or above the mandate cap
`A2M_FAT_FINGER_NOTIONAL`	`APEX_4011`	Notional above the mandate cap
`A2M_KILL_HALT`	`APEX_4023`	Kill switch is set to halt
`A2M_REDUCE_ONLY`	`APEX_4023`	Order would not reduce, or the account is reduce-only
`A2M_DAILY_LOSS`	`APEX_4022`	Daily loss limit reached; only reducing orders pass
`A2M_SHORT_DISABLED`	`APEX_4021`	Order would open or extend a short, or flip through flat
`A2M_POSITION_LIMIT`	`APEX_4021`	Projected position above the mandate limit
`A2M_MAX_OPEN`	`APEX_4021`	Too many open orders
`A2M_RATE_LIMIT`	`APEX_4040`	Order rate limit reached
`A2M_BUYING_POWER`	`APEX_4020`	Buying power below the required reservation
`A2M_BUDGET`	`APEX_4020`	The mandate’s budget cannot cover the reservation
`A2M_ACCOUNT_CASH`	`APEX_4020`	Broker cash unknown or insufficient

An approval that ends without an executable decision carries A2M_APPROVAL_DENIED (a human declined) or A2M_APPROVAL_EXPIRED (nobody answered in time).

HTTP errors

Code	HTTP	Meaning
`APEX_4001`	401	Bearer token missing or invalid
`APEX_4011`	400	Intent is malformed (for example an unknown `time_in_force` or a JSON number in a money field)
`A2M_IDEMPOTENCY`	409	`intent_id` reused for a different order
`A2M_BAD_SIGNATURE`	422	Decision signature did not verify
`A2M_BAD_DECISION`	422	Decision payload is malformed or uses an unknown version or field
`A2M_NOT_AUTHORIZED`	422 / 404 / 409	Decision is not executable, or unknown
`A2M_ENFORCEMENT`	422	Enforcement mode not supported by this executor
`A2M_DECISION_EXPIRED`	422	Decision expired before send
`A2M_DECISION_CONSUMED`	409	Decision was already sent
`A2M_NO_ROUTE`	422	Executor has no connection to the venue
`A2M_ORDER_TYPE`, `A2M_TIME_IN_FORCE`	422	Venue capabilities do not include this order type or time in force
`A2M_VENUE_DOWN`	503	Venue unavailable, or capabilities unreadable; fail closed
`A2M_ORDER_STATE`	409 / 404	Illegal state transition, or unknown order
`A2M_BLIND_RESEND`	409	Refusing to resend after an unknown or in-flight submit
`A2M_APPROVAL`	404 / 409	Unknown approval, or already decided
`A2M_RATE_LIMIT`	429	Too many requests for this credential
`A2M_UPSTREAM`	503	A service behind the gateway is unavailable
`A2M_INTERNAL`	500	Internal error

Control-plane codes (A2M_TENANT, A2M_USER, A2M_ACCOUNT, A2M_OAUTH_BINDING, A2M_RESERVATION, A2M_EVIDENCE) are implementation-specific and not part of v0.1.