Error codes

Machine-readable error taxonomy with suggested actions.

Every Sly error response has a stable code field. Your integration should branch on code, not on human-readable message text.

Response shape

{
  "error": "Insufficient balance",
  "code": "INSUFFICIENT_BALANCE",
  "details": {
    "required": "100.00",
    "available": "42.50",
    "currency": "USDC"
  },
  "request_id": "req_..."
}

code is always one of the enum values below. details varies per code and carries the contextual info you need to act.

Categories

Balance errors (400)

• INSUFFICIENT_BALANCE — spend > available
• HOLD_EXCEEDS_BALANCE — a hold would exceed available
• CURRENCY_MISMATCH — source and destination currencies don’t match (cross-border needs a quote)
• NEGATIVE_BALANCE_NOT_ALLOWED — operation would leave a negative balance

Validation (400, 422)

• INVALID_AMOUNT, INVALID_CURRENCY
• INVALID_ACCOUNT_ID, INVALID_AGENT_ID, INVALID_TRANSFER_ID
• INVALID_PIX_KEY, INVALID_CLABE, INVALID_IBAN, INVALID_SWIFT_CODE
• INVALID_EMAIL, INVALID_PHONE
• INVALID_DATE_RANGE, INVALID_FLOW_RATE
• INVALID_MANDATE, INVALID_CHECKOUT_SESSION
• MISSING_REQUIRED_FIELD, INVALID_REQUEST_FORMAT
• AMOUNT_TOO_SMALL, AMOUNT_TOO_LARGE

Authentication (401)

• INVALID_API_KEY — key not recognized
• EXPIRED_API_KEY — key revoked
• INVALID_AGENT_TOKEN, INVALID_SESSION_TOKEN
• SESSION_EXPIRED — re-run Ed25519 handshake
• INVALID_JWT, EXPIRED_JWT
• MISSING_AUTH_HEADER, MALFORMED_AUTH_HEADER
• ENVIRONMENT_MISMATCH — test key on prod URL (or vice versa)

Authorization (403)

• FORBIDDEN — generic “not allowed”
• INSUFFICIENT_SCOPE — API key lacks required scope
• KYA_LIMIT_EXCEEDED — agent KYA tier limit exceeded
• KYC_LIMIT_EXCEEDED — account KYC tier limit exceeded
• POLICY_VIOLATION — wallet policy rule violation
• WALLET_FROZEN — wallet frozen, cannot spend
• AGENT_SUSPENDED — agent suspended
• MERCHANT_BLOCKED — merchant blocked by policy
• VELOCITY_EXCEEDED — too many tx in window
• TIME_RULE_VIOLATION — outside allowed hours
• REQUIRES_APPROVAL — approval workflow triggered (not an error — next step is /v1/approvals)

Not found (404)

• ACCOUNT_NOT_FOUND, AGENT_NOT_FOUND, WALLET_NOT_FOUND, TRANSFER_NOT_FOUND
• STREAM_NOT_FOUND, QUOTE_NOT_FOUND, MANDATE_NOT_FOUND
• WEBHOOK_NOT_FOUND

Conflict (409)

• IDEMPOTENCY_KEY_REUSED — same key with different parameters
• DUPLICATE_RESOURCE — resource with same unique key already exists
• STATE_TRANSITION_INVALID — operation not allowed in current state (e.g. completing a cancelled transfer)

Quote / settlement (400, 402)

• QUOTE_EXPIRED
• QUOTE_RATE_CHANGED
• SETTLEMENT_RAIL_UNAVAILABLE
• RAIL_DECLINED, RAIL_TIMEOUT
• X402_PAYMENT_REQUIRED — 402 returned by an x402-gated endpoint (includes payment quote)
• X402_PROOF_INVALID, X402_PROOF_EXPIRED

Rate limit (429)

• RATE_LIMIT_EXCEEDED — honor Retry-After

Server (500, 502, 503, 504)

• INTERNAL_ERROR — retry with backoff
• SERVICE_UNAVAILABLE — retry with backoff
• UPSTREAM_TIMEOUT — retry with backoff
• DATABASE_ERROR — retry; if persistent, open a support ticket

Compliance (400, 403)

• SANCTIONS_HIT — counterparty on sanctions list
• KYC_REQUIRED, KYB_REQUIRED
• HIGH_RISK_TRANSACTION — manual review triggered
• BLOCKED_COUNTRY, BLOCKED_ADDRESS

Suggested actions

The error object often includes suggested_action:

{
  "code": "KYA_LIMIT_EXCEEDED",
  "details": {
    "limit": "500.00",
    "attempted": "750.00",
    "current_tier": 1,
    "tier_ceiling": "500.00"
  },
  "suggested_action": {
    "type": "tier_upgrade",
    "endpoint": "/v1/agents/agt_.../upgrade-tier",
    "documentation_url": "/agents/kya-tiers"
  }
}

Use this to guide your error UX — for humans, surface the doc link; for agents, the endpoint can be invoked directly to self-remediate.

Retriable vs. permanent

Retriable (with backoff):

• RATE_LIMIT_EXCEEDED
• INTERNAL_ERROR, SERVICE_UNAVAILABLE, UPSTREAM_TIMEOUT, DATABASE_ERROR

Everything else is permanent for this request — retrying won’t help. Fix the input or escalate.

Request ID

Every error response carries request_id. Include this in support tickets; we can pull the full trace in seconds.