I was looking though the documentation and I don't see any webhooks being offered. It would be nice to have some webhooks especially for unsubscribes and list removals.
Thank you for reaching out to Constant Contact API Developer Support.
Unfortunately our API does not offer webhooks. We do offer an updated subscriber email to be sent to an account owner on a daily or weekly basis. This email includes newly added contacts as well as those who have unsubscribed. For details on this email, see: https://knowledgebase.constantcontact.com/articles/KnowledgeBase/5530-automatic-email-updates-for-si...
I will make sure this feedback gets to our product management team for consideration.
Sincerely,David B.Tier II API Support Engineer