Customer.io Common Errors

Overview

Diagnose and fix the most frequent Customer.io integration errors: API status codes, SDK exceptions, delivery failures, campaign trigger issues, and transactional message problems.

Prerequisites

• Access to Customer.io dashboard
• API credentials configured
• Access to application logs

HTTP Status Code Reference

Code	Meaning	Retryable	Action
200	Success	N/A	No action needed
400	Bad Request	No	Fix request payload — see details below
401	Unauthorized	No	Check API credentials
403	Forbidden	No	API key lacks permission for this endpoint
404	Not Found	No	Check endpoint URL or resource ID
408	Request Timeout	Yes	Retry with backoff
422	Unprocessable Entity	No	Validation error — check required fields
429	Rate Limited	Yes	Back off, respect Retry-After header
500	Internal Server Error	Yes	Retry with exponential backoff
503	Service Unavailable	Yes	Check status.customer.io, retry later

Instructions

Error 1: Authentication Failures (401/403)

// WRONG — mixing up API key types
import { TrackClient, APIClient, RegionUS } from "customerio-node";

// Track API uses Site ID + Track API Key (Basic Auth)
const cio = new TrackClient(siteId, trackApiKey, { region: RegionUS });

// App API uses App API Key (Bearer Auth) — DIFFERENT key
const api = new APIClient(appApiKey, { region: RegionUS });

// Common mistake: using Track API key for App API client
// const api = new APIClient(trackApiKey); // WRONG — will get 401

Fix: Verify you're using the right key type. Track API credentials are under "Tracking API Key" in Settings. App API key is under "App API Key" — it's a separate bearer token.

Error 2: Timestamp Format (400)

// WRONG — Customer.io expects Unix seconds, not milliseconds
await cio.identify("user-1", {
  created_at: Date.now(),              // 1704067200000 — TOO LARGE
});

// CORRECT — divide by 1000
await cio.identify("user-1", {
  created_at: Math.floor(Date.now() / 1000),  // 1704067200
});

Customer.io silently accepts millisecond timestamps but interprets them as dates thousands of years in the future, breaking segment conditions and campaign triggers.

Error 3: Events Not Triggering Campaigns

// WRONG — event name doesn't match dashboard
await cio.track("user-1", { name: "SignedUp", data: {} });
// Dashboard expects: "signed_up" (case-sensitive)

// CORRECT — exact match, snake_case
await cio.track("user-1", { name: "signed_up", data: {} });

Checklist:

1. Event name is case-sensitive — must match dashboard trigger exactly
2. User must be identified before tracking (call identify() first)
3. Campaign must be Active (not Draft or Paused)
4. User must match campaign's audience filter/segment
5. User must not be suppressed

Error 4: Transactional Message Failures (422)

import { APIClient, SendEmailRequest, RegionUS } from "customerio-node";

const api = new APIClient(process.env.CUSTOMERIO_APP_API_KEY!, {
  region: RegionUS,
});

// Common 422 errors:
// 1. Wrong transactional_message_id
const request = new SendEmailRequest({
  to: "user@example.com",
  transactional_message_id: "999",     // Must exist in dashboard
  message_data: { name: "Jane" },
  identifiers: { id: "user-123" },
});

// 2. Missing required message_data fields
// If template uses {{ data.reset_url }}, message_data must include reset_url

// 3. Invalid email address
// "to" must be a valid email format

Error 5: Rate Limiting (429)

// Implement backoff when you hit 429
async function withBackoff<T>(fn: () => Promise<T>, maxRetries = 3): Promise<T> {
  for (let i = 0; i <= maxRetries; i++) {
    try {
      return await fn();
    } catch (err: any) {
      if (err.statusCode === 429 && i < maxRetries) {
        // Respect Retry-After header if present, otherwise exponential backoff
        const retryAfter = err.headers?.["retry-after"];
        const delay = retryAfter
          ? parseInt(retryAfter) * 1000
          : Math.pow(2, i) * 1000 + Math.random() * 500;
        console.warn(`Rate limited. Retrying in ${delay}ms...`);
        await new Promise((r) => setTimeout(r, delay));
        continue;
      }
      throw err;
    }
  }
  throw new Error("Max retries exceeded");
}

// Usage
await withBackoff(() => cio.identify("user-1", { email: "user@example.com" }));

Error 6: EU Region Mismatch

// WRONG — EU account hitting US endpoint
const cio = new TrackClient(siteId, apiKey, { region: RegionUS });
// Returns 401 because credentials are for EU workspace

// CORRECT
import { RegionEU } from "customerio-node";
const cio = new TrackClient(siteId, apiKey, { region: RegionEU });

Error 7: User Not Receiving Email

Diagnostic checklist:

1. Does the user have an email attribute? (Check People > user profile)
2. Is the user suppressed? (Check suppression list)
3. Has the email bounced before? (Check user Activity tab)
4. Is the campaign Active? (Check Campaigns list)
5. Does the user match the segment? (Check segment membership)
6. Is the sending domain verified? (Settings > Sending Domains)

Diagnostic Commands

# Test Track API authentication
curl -s -w "\nHTTP %{http_code}\n" \
  -u "$CUSTOMERIO_SITE_ID:$CUSTOMERIO_TRACK_API_KEY" \
  -X PUT "https://track.customer.io/api/v1/customers/test-diag" \
  -H "Content-Type: application/json" \
  -d '{"email":"diag@example.com"}'

# Test App API authentication
curl -s -w "\nHTTP %{http_code}\n" \
  -H "Authorization: Bearer $CUSTOMERIO_APP_API_KEY" \
  "https://api.customer.io/v1/campaigns"

# Check Customer.io status
curl -s "https://status.customer.io/api/v2/status.json" | python3 -m json.tool

Error Handling Pattern

// Centralized error handler for Customer.io operations
async function safeCioCall<T>(
  operation: string,
  fn: () => Promise<T>
): Promise<T | null> {
  try {
    return await fn();
  } catch (err: any) {
    const code = err.statusCode ?? err.status ?? "unknown";
    console.error(`CIO ${operation} failed [${code}]:`, err.message);

    // Alert on auth errors — likely misconfiguration
    if (code === 401 || code === 403) {
      console.error("AUTH ERROR: Check API credentials immediately");
    }

    // Don't crash the app for tracking failures
    return null;
  }
}

// Usage — never crashes your app
await safeCioCall("identify", () =>
  cio.identify("user-1", { email: "user@example.com" })
);

Resources

• Track API Error Reference
• Common Transactional API Errors
• Common Broadcast Errors
• Customer.io Status Page

Next Steps

After resolving errors, proceed to customerio-debug-bundle for comprehensive debug reports.