Customer.io has two APIs: the Track API (https://track.customer.io/api/v1) records people and events, and the App API (https://api.customer.io/v1) sends transactional messages and reads data. EU accounts use -eu hosts.
The Track API uses Basic auth with your Site ID and Track API key — curl's -u, PostTaco's Auth tab. The App API uses an App API key as a Bearer token. Both are under Account Settings → API Credentials.
Full reference: https://docs.customer.io/api/
curl -X PUT https://track.customer.io/api/v1/customers/user-123 \
-u {{CIO_SITE_ID}}:{{CIO_TRACK_API_KEY}} \
-H "Content-Type: application/json" \
-d '{"email": "[email protected]", "plan": "pro"}'curl -X POST https://track.customer.io/api/v1/customers/user-123/events \
-u {{CIO_SITE_ID}}:{{CIO_TRACK_API_KEY}} \
-H "Content-Type: application/json" \
-d '{"name": "purchased", "data": {"price": 23.45}}'Uses a transactional message template.
curl -X POST https://api.customer.io/v1/send/email \
-H "Authorization: Bearer {{CIO_APP_API_KEY}}" \
-H "Content-Type: application/json" \
-d '{"transactional_message_id": "{{MESSAGE_ID}}", "to": "[email protected]", "identifiers": {"id": "user-123"}}'