We've started writing over the campaign_id or outreach_id values on Orders to align with our new attribution model and user-configured settings. If your integration is sending campaign_id or outreach_id with Add Order or Update Order API calls, we recommend deprecating that logic.

We’re rolling out Mailchimp's native attribution model across all e-commerce integrations. This new model gives you more complete insights into how marketing campaigns contribute to customer purchases. It also improves marketing performance reporting for all Mailchimp customers using e-commerce integrations. Additionally, this reduces the need for complex custom logic for attributing orders to specific marketing messages.