Errors

Every 4xx and 500 response (except 429) is the same JSON object:

{
  "code": "insufficient_funds",
  "message": "The source account has $120.00 available but this transfer needs $500.00.",
  "details": {
    "available": "$120.00",
    "requested": "$500.00"
  },
  "referenceId": "4009-2alj5if"
}

Field	Use
`code`	Machine-readable reason. Branch on the HTTP status and this.
`message`	Human-readable context for an operator. Wording may become more specific over time; do not parse it.
`details`	The values behind `message`, as strings keyed per `code` — for example the field that failed validation, or the amounts behind `insufficient_funds`. `{}` when the code carries no variable data.
`referenceId`	Uniquely identifies the failure on Slash’s side. Include it when contacting support, especially about a `500`.

Errors every endpoint can return

These are raised at the boundary — authentication, request parsing, resource lookup — before or around the operation itself, so every endpoint can return them. Each reference page lists them alongside the endpoint’s own codes, grouped by status; this table is where they are explained once.

Status	Code	When
`400`	`invalid_request`	The body, query, or headers failed validation, or a required header such as `X-Idempotency-Key` is missing. `details` has one entry per failing location, keyed by JSON pointer (for example `/amount/amount`) or header name.
`401`	`unauthorized`	API key authentication is missing or invalid.
`403`	`forbidden`	The credential is not permitted to perform this action. Also returned when the credential is scoped to another legal entity.
`403`	`user_api_key_required`	The API key is scoped to a legal entity rather than a user. v2 only accepts user API keys.
`403`	`not_available`	Public API v2 is not yet available. The credential and request are fine; use Public API v1 in the meantime.
`404`	`not_found`	No resource matches the identifier. When the identifier is a field inside a request body (for example `destinationId` on a transfer), `details` names that `field` and the `id` it received.
`409`	`conflict`	A consumed `X-Idempotency-Key` was reused on an endpoint that takes one. The original response is not replayed; see Idempotency.
`429`	—	The caller exceeded an applicable rate limit. The body is plain text, not the object above.
`500`	`internal`	Slash could not complete the request.

Errors specific to an endpoint

Each reason an operation itself can refuse has its own code — insufficient funds, an expired FX quote, a transfer that can no longer be canceled, a money-movement action that needs an IP allowlist. They are listed first under their status on the endpoint’s reference page, with the message you will see. For example, Create an ACH transfer lists insufficient_funds and destination_archived next to conflict under 409, and ip_allowlist_required next to forbidden under 403. An endpoint never returns a code it does not list. When a reason is about a field of the request, details.field names it and, when that field carries an identifier, details.id holds the value received. The reference page shows one example for each field an endpoint can name.

Retry behavior

Retry

Retry idempotent reads after 429 or 500 responses with exponential backoff and random jitter.

Fix before retrying

Change the request or credentials before retrying 400, 401, 403, or 404 responses.

For a timed-out create request or a create request that returns 500, do not retry automatically. Its idempotency key may already be permanently consumed. Follow the idempotency guidance and reconcile through the resource’s list and retrieve endpoints before deciding whether to make a new create attempt.

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Working with the API

Core objects

Money movement

Cards

Bill pay

Invoicing

Accounting

Errors every endpoint can return

Errors specific to an endpoint

Retry behavior

Retry

Fix before retrying

​Errors every endpoint can return

​Errors specific to an endpoint

​Retry behavior

Retry

Fix before retrying

Errors every endpoint can return

Errors specific to an endpoint

Retry behavior