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Overview

Spending controls let you set guardrails on your ACN account. This is especially useful when running autonomous agents that make API calls without human supervision. You can configure:
  • Daily spend limit — block all calls once your daily budget is used up
  • Per-call limit — block calls that cost more than a set threshold
  • Low-balance alert — get an email before your credits run out
All limits are checked in real-time before each call executes.

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Daily Spend Limit

Sets the maximum credits your account can spend in a single UTC calendar day. Once hit, all subsequent calls return HTTP 402 until the day resets at midnight UTC. Example: Set a $50/day limit to prevent an agent from accidentally spending more than your daily budget.

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From the Dashboard

  1. Go to Billing → Spending Controls
  2. Toggle on Daily Spend Limit
  3. Enter your limit in USD (e.g., 50.00)
  4. Click Save

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Via API

curl -X PUT https://api.acn.exchange/v1/billing/limits \
  -H "Authorization: Bearer acn_sk_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "dailySpendLimitUsdc": "50.00"
  }'
Response: 
{
  "dailySpendLimitCredits": "50000000",
  "dailySpendLimitUsdc": "50.000000",
  "perCallLimitCredits": null,
  "perCallLimitUsdc": null
}
To remove the daily limit, pass null: 
-d '{"dailySpendLimitUsdc": null}'

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What Happens When the Limit is Reached

Calls are rejected with HTTP 402 before they reach the provider: 
{
  "statusCode": 402,
  "code": "ACN-CREDIT-002",
  "error": "Spending Limit Exceeded",
  "message": "Daily spending limit of 50,000,000 credits ($50.00) would be exceeded.",
  "details": {
    "limitType": "daily",
    "limitCredits": "50000000",
    "currentDailySpend": "49500000",
    "requestedCredits": "2000000"
  }
}
The limit resets at midnight UTC each day.

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Per-Call Limit

Blocks any single call that costs more than your threshold. Useful for preventing unexpectedly expensive capabilities from draining your balance. Example: Set a $0.50 per-call limit to ensure no single call costs more than 50 cents.

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Via Dashboard

Billing → Spending Controls → toggle Per-Call Limit → enter amount → Save.

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Via API

curl -X PUT https://api.acn.exchange/v1/billing/limits \
  -H "Authorization: Bearer acn_sk_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "perCallLimitUsdc": "0.50"
  }'
You can set both limits at once: 
-d '{
  "dailySpendLimitUsdc": "50.00",
  "perCallLimitUsdc": "0.50"
}'

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Low Balance Alert

Sends an email when your credit balance drops below a threshold. Use this to top up before calls start failing.
Alerts are sent at most once every 24 hours per threshold to avoid inbox spam.

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Via Dashboard

Billing → Notifications → set Low Balance Threshold (e.g., 5.00 USDC) → Save.

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Via API

curl -X PUT https://api.acn.exchange/v1/billing/alerts \
  -H "Authorization: Bearer acn_sk_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "lowBalanceThresholdUsdc": "5.00",
    "emailNotifications": {
      "lowBalance": true
    }
  }'

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Checking Current Limits

curl https://api.acn.exchange/v1/billing/balance \
  -H "Authorization: Bearer acn_sk_your_key"

{
  "balanceCredits": "8500000",
  "balanceUsdc": "8.500000",
  "dailySpentCredits": "1200000",
  "dailySpentUsdc": "1.200000",
  "dailySpendLimitCredits": "50000000",
  "dailySpendLimitUsdc": "50.000000",
  "perCallLimitCredits": "500000",
  "perCallLimitUsdc": "0.500000"
}
For production agents running without supervision: 
# Set a $25/day daily limit and $0.10 per-call cap
# Alert when balance drops below $5
curl -X PUT https://api.acn.exchange/v1/billing/limits \
  -H "Authorization: Bearer acn_sk_your_key" \
  -d '{
    "dailySpendLimitUsdc": "25.00",
    "perCallLimitUsdc": "0.10"
  }'

curl -X PUT https://api.acn.exchange/v1/billing/alerts \
  -H "Authorization: Bearer acn_sk_your_key" \
  -d '{
    "lowBalanceThresholdUsdc": "5.00",
    "emailNotifications": {
      "lowBalance": true,
      "dailyLimitReached": true,
      "unusualActivity": true
    }
  }'
This setup:
  • Caps daily exposure at $25
  • Prevents calls to high-cost endpoints that exceed $0.10
  • Alerts you when you need to top up
  • Notifies you if usage spikes unexpectedly (potential key compromise)