Hello,
In order to insert the Constant Contact contactId into the body of an email, you would need to retrieve the contactId and then add it as a Custom Field within the contact in order to use it as part of a Dynamic Link. We don't currently offer a way to insert the contactId directly into an email campaign.
Bulk Activities - Export Contacts Endpoint https://v2.developer.constantcontact.com/docs/bulk_activities_api/bulk-activities-export-contacts.html
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