How do I insert data from an event attribute (like a promo code) into an email sent via Customer Journey?

You can use data from the event that triggers a Customer Journey to personalize the emails sent within that journey. There are two separate mechanisms, and the placeholder syntax differs between them — mixing them up is the usual reason a promo code comes out blank.

Option A — Personalise message with event attributes (mapped placeholders)

1. Start the journey with a Trigger-based entry, selecting the event that carries your data (for example Coupon_Generated with an attribute coupon_code).
2. Add a Send Email element after it.
3. In the element's Overwrite personalization section, enable Personalise message with event attributes.
4. Map the event attribute (coupon_code) to a placeholder Name — for example promo_placeholder.
5. In the email template, reference the placeholder by the Name you mapped, as a bare key: {{ promo_placeholder }}.

Option B — Overwrite Liquid placeholders (raw event attribute names)

1. In the same Overwrite personalization section, enable Overwrite Liquid placeholders and select the Event.
2. Every attribute of that event becomes available under its own attribute name, so in the template you write {{ coupon_code }}.
3. With this mode, the placeholder name must match an existing Tag name for template validation to pass — the value is still taken from the event at send time.

Important — syntax that does NOT work

• {{ custom_data.promo_placeholder }} — there is no custom_data namespace; this renders as an empty string.
• {{ event.coupon_code }} — there is no event namespace either. Drop the prefix and use {{ coupon_code }}.

Event attributes are only available as placeholders in the Customer Journey event-triggered path. If you send via the API instead (for example createEmailMessage against a segment), there is no event context at all — pass the value explicitly in the request body (dynamic_content_placeholders).

Also note that Liquid {{ }} rendering must be enabled for your account; if your placeholders come through literally, contact support to confirm it is switched on.

Learn more: Dynamic Content and Liquid Templates in journeys