Errors

Every error has the same shape:

{
  "success": false,
  "error": "validation_failed",
  "detail": "One or more fields are invalid.",
  "fields": [ { "path": "sizing.ratio", "code": "less_than_equal", "limit": 10 } ],
  "meta": { "requestId": "req_9f2c1a0b7d3e4f51" }
}

• error is a stable code from the tables below. Build your logic on it.
• detail is a plain-English sentence you can show to a person. Its wording can change.
• fields appears on validation errors and on a few other errors that point at specific fields (for example account_not_found on connection settings, field_locked and switches_locked). path is the field (dotted for nested fields, for example sizing.ratio), code says what is wrong, and limit or pattern shows the bound that was broken. The values you sent are never repeated back.
• retryAfter (seconds) and a Retry-After header accompany 429 admission refusals and 503 management_busy, and can accompany 409 concurrent_modification. Other 503 errors may omit them. policy names the budget on rate_limited.
• meta.etag comes with 412 precondition_failed and holds the current ETag.

Request and access errors

Status	error	Meaning	What to do
400	invalid_json	The body is not valid JSON, has duplicate keys, NaN/Infinity, or is nested too deeply	Fix the body
400	unexpected_body	A GET or DELETE was sent with a body	Send no body
400	unknown_parameter	An unknown or repeated query parameter	Remove it
400	invalid_path	The account name or id in the path is not valid	Check the encoding and the value
401	unauthorized	Missing, malformed or revoked token, or a disabled account	Check the Authorization: Bearer header
403	elite_required	Your plan does not include the Management API	Upgrade to Elite
403	not_available	The Management API is not open for your account yet	Contact support
403	plan_required	Your plan does not include this feature	Upgrade your plan
404	not_found	No such resource on your account, or an unknown endpoint	Check the path and id
405	method_not_allowed	The endpoint exists but not with that method. The Allow header lists the methods it takes	Use an allowed method
408	body_timeout	The body was not received within 10 seconds	Retry
413	body_too_large	The body is larger than 64 KB	Send a smaller body
415	unsupported_content_type	The body is not application/json, declares a charset other than UTF-8, or is compressed	Send uncompressed UTF-8 JSON
429	rate_limited	A budget is used up	Wait retryAfter seconds. See Rate limits
429	too_many_concurrent_requests	Two requests are already running for your account	Wait for one to finish
500	internal_error	Something went wrong on our side	Retry later; contact support with the request id
503	management_unavailable	The Management API is temporarily off	Retry later
503	management_read_only	Changes are temporarily paused; reads still work	Retry later
503	family_unavailable	This part of the API is temporarily off	Retry later
503	management_busy	The API is under heavy load	Wait retryAfter seconds

Validation errors (422)

error	Meaning	What to do
validation_failed	One or more fields are invalid. fields lists each problem	Fix the listed fields
field_read_only	The body contains a field you cannot change (for example id or state)	Remove it, or send the saved value
field_not_applicable	The field does not exist for this broker (for example a NinjaTrader-only monitor field on a Tradovate monitor)	Remove it
immutable_field	The field can only be set when the resource is created (a monitor's account, an account group's destination)	Delete and re-create instead
use_kill_switch_endpoint	killSwitch was sent to PATCH /controls with a value different from the saved one	Use PUT /controls/kill-switch
invalid_replacement	A copier symbol replacement is not allowed	See the copier field reference
invalid_atm_config	The ATM template configuration is not valid. detail names the problem and fields lists the config.* fields involved	Fix the named fields

On a create, field_read_only and field_not_applicable refuse the field whatever its value. On a PATCH, field_read_only, immutable_field, use_kill_switch_endpoint and field_not_applicable mean the value you sent differs from what is saved: a matching value is ignored, so you can send back a resource you just read.

Common code values in fields for validation_failed:

code	Meaning
required_when_days_set	The master trading window has days but no start or end
required_when_enabled	The setting is turned on but the value it needs is missing or zero (for example a trailing drawdown with amount: 0, which would stop the account on the first tick)
empty_window	A trading window starts and ends at the same time, which would allow trading for one minute a day
outside_window	closingOnlyAfter is not strictly inside the master trading window (which runs past midnight when end is earlier than start)
windows_overlap	Two enabled monitor trading windows cover the same time
ratio_not_a_step	A copier ratio is not one of the values the web app offers (0.25 to 1.75 in steps of 0.25, then 2 to 10)
unknown_connection	A connection name is not one of your NinjaTrader connections
string_pattern_mismatch	The value does not match the format, for example a time that is not on a 5-minute mark

Conflicts and state errors

Status	error	Meaning	What to do
409	already_exists	A monitor already exists for this account	Update it instead
409	concurrent_modification	Another change to the same kind of resource is in progress	Retry after about a second
409	addon_disconnected	The change needs your NinjaTrader add-on connected (for example to check that an account is yours)	Connect the add-on and retry
409	addon_version_unsupported	The change needs a newer add-on	Update the add-on
404	account_not_found	The account is not on your connection. On connection settings, fields lists where the unknown ones are	Check the account name
409	account_identity_unresolved	The Tradovate account could not be matched to your linked login	Check the name, or re-link Tradovate
409	tradovate_not_linked	Your Tradovate login is not linked	Link Tradovate in the web app
409	monitor_locked	Monitor Lock is on and the account reached a limit today	Wait for the 5:00 to 6:00 PM ET window, or turn Monitor Lock off
409	monitor_stopped_use_restart	The monitor is stopped and active: true cannot resume it	Use the restart endpoint
409	monitor_not_stopped	Restart was called on a monitor that is not stopped	Nothing to do
409	would_retrip	Restarting now would stop the monitor again right away	Adjust the limit first
409	tandem_dependency	The account is a follower in a Tandem copier	Turn off Tandem or remove that copier first
409	tandem_requires_monitor	Tandem needs a monitor on every follower account	Create the monitors first
409	copier_cycle	The copier would create a copy loop. Inactive copiers count	Change the leader or followers
409	duplicate_copier	A copier from this leader to this follower already covers these instruments, even if that copier is inactive	Edit the existing copier
409	duplicate_follower	A follower appears more than once	Remove the duplicate
409	follower_conflict	The follower is already used by another copier in a conflicting way	Change the follower
409	autosync_conflict	Two Auto-Sync copiers would manage the same follower and instrument	Turn off Auto-Sync on one, or split the instruments
409	group_name_conflict	The name is already used by another group or by an account	Choose another name
409	group_limit_reached	You have the maximum number of account groups	Delete a group first
409	template_name_conflict	An ATM template with this name exists	Choose another name
409	limit_reached	You reached the maximum allowed for this resource	Remove or pause one first
409	field_locked	This setting is managed by another feature on this account	Change it where that feature is configured
409	switches_locked	blockSignals or closingOnly was changed on a monitor whose switches are locked (switchesLocked: true)	Send switchesLocked: false in the same request, or unlock first
412	precondition_failed	If-Match did not strongly match: the resource changed, or you supplied a weak tag	Read it again and use the current strong ETag in meta.etag

When the outcome is uncertain

Status	error	Meaning	What to do
503	storage_unavailable	The change could not be saved and nothing was applied	Retry shortly
503	outcome_unknown	The change may or may not have been applied	Read the resource before retrying