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Customer.io

Estimated reading: 2 minutes Updated August 1, 2026

Customer.io is a behavioral messaging platform popular with SaaS for cross-channel email, push, SMS, and in-app messages. Advanced Form Integration sends form submissions to Customer.io as new people via the Identify endpoint.

What you’ll need

  • An active Customer.io workspace.
  • Customer.io Site ID and Track API Key (Settings → Account Settings → API Credentials → Track API Keys).
  • Your Customer.io region (US or EU; they have separate API endpoints).
  • The Advanced Form Integration plugin installed and activated.

Connect Customer.io to AFI

  1. In WordPress, go to AFI → Settings → Customer.io.
  2. Enter the Site ID, Track API Key, and pick the region.
  3. Click Save Changes.

Create the integration

  1. Go to AFI → Add New.
  2. Configure the trigger.
  3. In Action → Platform, select Customer.io.
  4. In Task, choose Identify Person or Track Event.
  5. Map the form fields:
  • ID (your app’s user identifier, required for identify) or Email.
  • First Name, Last Name, Created At (Unix timestamp), Phone.
  • For Track Event: Event Name plus typed event properties.
  • Custom attributes by name.
  1. Optional: configure Conditional Logic.
  2. Click Save Integration.

Screenshot: AFI field-mapping screen with Customer.io person fields visible

Conditional logic example

Track a webinar_signup event only when the form is the webinar registration form. Newsletter signups instead trigger an subscribed event via a separate integration.

Troubleshooting

“Unauthorized”

Customer.io has multiple API key types. Use the Track API Key (paired with Site ID) for identify/track; the App API Key is for transactional sends and won’t work here.

Email-only person

If you don’t supply id, Customer.io creates an anonymous-style user keyed by email. This can complicate later identification. Prefer using your app’s stable user ID where possible.

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