Customer.io Known Pitfalls
Overview
The 12 most common Customer.io integration mistakes, with the wrong pattern, the correct pattern, and why it matters. Use this as a code review checklist and developer onboarding reference.
The Pitfall Catalog
Pitfall 1: Wrong API Key Type
// WRONG — using Track API key for transactional messages
const api = new APIClient(process.env.CUSTOMERIO_TRACK_API_KEY!);
// Gets 401 because App API uses a DIFFERENT bearer token
// CORRECT — use the App API key
const api = new APIClient(process.env.CUSTOMERIO_APP_API_KEY!);
Why: Customer.io has two separate authentication systems. Track API uses Basic Auth (Site ID + Track Key). App API uses Bearer Auth (App Key). They are not interchangeable.
Pitfall 2: Millisecond Timestamps
// WRONG — JavaScript Date.now() returns milliseconds
await cio.identify("user-1", {
created_at: Date.now(), // 1704067200000 → year 55976
});
// CORRECT — Customer.io expects Unix seconds
await cio.identify("user-1", {
created_at: Math.floor(Date.now() / 1000), // 1704067200
});
Why: Customer.io accepts millisecond values without error but interprets them as seconds, resulting in dates thousands of years in the future. Segments using date comparisons silently break.
Pitfall 3: Track Before Identify
// WRONG — tracking before identifying creates orphaned events
await cio.track("new-user", { name: "signed_up", data: {} });
// User profile doesn't exist yet — event may be lost
// CORRECT — always identify first
await cio.identify("new-user", { email: "user@example.com" });
await cio.track("new-user", { name: "signed_up", data: {} });
Why: Track calls on non-existent users may be silently dropped. Always identify() before track().
Pitfall 4: Using Email as User ID
// WRONG — email can change, creating duplicate profiles
await cio.identify("user@example.com", { email: "user@example.com" });
// When user changes email, old profile orphaned, new one created
// CORRECT — use immutable database ID
await cio.identify("usr_abc123", {
email: "user@example.com", // Email as attribute, not ID
});
Why: The first argument to identify() is the permanent user ID. If you use email and the user changes it, you get two profiles. Use your database primary key instead.
Pitfall 5: Missing Email Attribute
// WRONG — user can't receive email campaigns
await cio.identify("user-1", {
first_name: "Jane",
plan: "pro",
// No email attribute!
});
// CORRECT — always include email for email campaigns
await cio.identify("user-1", {
email: "jane@example.com",
first_name: "Jane",
plan: "pro",
});
Why: Without an email attribute, the user profile exists but can't receive any email campaigns or transactional messages.
Pitfall 6: Dynamic Event Names
// WRONG — creates hundreds of unique event names
await cio.track("user-1", {
name: `viewed_${productId}`, // "viewed_SKU-12345"
data: {},
});
// CORRECT — use a static name with data properties
await cio.track("user-1", {
name: "product_viewed", // Consistent, filterable
data: { product_id: productId }, // Dynamic data in properties
});
Why: Dynamic event names pollute your event catalog and make it impossible to create campaign triggers. Use a fixed set of event names and pass variations as data properties.
Pitfall 7: Blocking Request Path
// WRONG — API call adds 200ms+ to every request
app.post("/api/action", async (req, res) => {
const result = await doBusinessLogic(req.body);
await cio.track(req.user.id, { name: "action_taken", data: {} }); // BLOCKS response
res.json(result);
});
// CORRECT — fire-and-forget for non-critical tracking
app.post("/api/action", async (req, res) => {
const result = await doBusinessLogic(req.body);
cio.track(req.user.id, { name: "action_taken", data: {} })
.catch((err) => console.error("CIO track failed:", err.message));
res.json(result); // Returns immediately
});
Why: Customer.io tracking is non-critical analytics. Don't add 200ms+ latency to every user request.
Pitfall 8: No Bounce Handling
// WRONG — keep sending to bounced addresses, damaging sender reputation
// (No webhook handler for bounces)
// CORRECT — suppress users who bounce
async function handleBounceWebhook(event: { customer_id: string }) {
await cio.suppress(event.customer_id);
console.warn(`Suppressed bounced user: ${event.customer_id}`);
}
Why: Continuing to send to bounced addresses damages your sender reputation, eventually causing all your emails to go to spam.
Pitfall 9: New Client Per Request
// WRONG — creates a new TCP connection for every API call
app.post("/track", async (req, res) => {
const cio = new TrackClient(siteId, apiKey, { region: RegionUS });
await cio.track(req.body.userId, req.body.event);
res.sendStatus(200);
});
// CORRECT — singleton, created once
const cio = new TrackClient(siteId, apiKey, { region: RegionUS });
app.post("/track", async (req, res) => {
await cio.track(req.body.userId, req.body.event);
res.sendStatus(200);
});
Why: Each new TrackClient() creates fresh connections. Singleton reuses TCP connections, reducing latency by 50-80%.
Pitfall 10: Inconsistent Event Names
// WRONG — multiple naming conventions
await cio.track(userId, { name: "UserSignedUp" }); // PascalCase
await cio.track(userId, { name: "user-signed-up" }); // kebab-case
await cio.track(userId, { name: "user signed up" }); // spaces
// CORRECT — consistent snake_case everywhere
await cio.track(userId, { name: "user_signed_up" });
Why: Event names are case-sensitive. Inconsistent naming means campaign triggers only match one variant, and your event catalog becomes a mess.
Pitfall 11: No Rate Limiting
// WRONG — blasting API at full speed during import
for (const user of allUsers) {
await cio.identify(user.id, user.attrs); // 1000+ req/sec → 429 errors
}
// CORRECT — rate-limited processing
import Bottleneck from "bottleneck";
const limiter = new Bottleneck({ maxConcurrent: 10, minTime: 15 });
for (const user of allUsers) {
await limiter.schedule(() => cio.identify(user.id, user.attrs));
}
Why: Customer.io rate limits at ~100 req/sec. Without throttling, bulk operations trigger 429 errors and potentially get your API key temporarily blocked.
Pitfall 12: PII in Event Names
// WRONG — PII in event names is unsanitizable
await cio.track(userId, { name: `email_sent_to_john@example.com` });
// CORRECT — PII only in data properties (can be deleted per GDPR)
await cio.track(userId, {
name: "email_sent",
data: { recipient: "john@example.com" },
});
Why: Event names are indexed and cached. PII in event names can't be deleted for GDPR compliance. Always put PII in event data properties.
Quick Reference
| # | Pitfall | Fix |
|---|---------|-----|
| 1 | Wrong API key type | Track key for tracking, App key for transactional |
| 2 | Millisecond timestamps | Math.floor(Date.now() / 1000) |
| 3 | Track before identify | Always identify() first |
| 4 | Email as user ID | Use immutable database ID |
| 5 | Missing email attribute | Include email in identify() |
| 6 | Dynamic event names | Static names, dynamic data properties |
| 7 | Blocking request path | Fire-and-forget with .catch() |
| 8 | No bounce handling | Suppress bounced users via webhook |
| 9 | New client per request | Singleton pattern |
| 10 | Inconsistent event names | Always snake_case |
| 11 | No rate limiting | Use Bottleneck or p-queue |
| 12 | PII in event names | PII in data properties only |
Integration Audit Script
# Quick grep audit for common pitfalls in your codebase
echo "=== Customer.io Pitfall Audit ==="
echo "--- Checking for Date.now() without /1000 ---"
grep -rn "created_at.*Date.now()" --include="*.ts" --include="*.js" \
| grep -v "/ 1000" || echo "OK"
echo "--- Checking for new TrackClient inside functions ---"
grep -rn "new TrackClient" --include="*.ts" --include="*.js" \
| grep -v "^.*const\|^.*let\|^.*export" || echo "OK"
echo "--- Checking for dynamic event names ---"
grep -rn "name:.*\`" --include="*.ts" --include="*.js" \
| grep "track\|Track" || echo "OK"
echo "--- Checking for blocking await in routes ---"
grep -rn "await.*cio\.\|await.*track\.\|await.*identify" --include="*.ts" \
| grep "router\.\|app\." || echo "Review these for fire-and-forget"
Resources
Next Steps
After reviewing pitfalls, use customerio-reliability-patterns for fault tolerance.