Hello user109669,
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
For sign-up form integrations, we typically recommend using the /sign_up_form endpoint, as it allows for an existing contact to have their profile updated with any new information being submitted, while the POST (create) request to the /contacts endpoint only allows for the creation of a new contact. If an existing contact’s information is submitted in a POST request to the /contacts endpoint, a 409 error is returned.
It is true that Confirm Opt-In is an account level setting that is applied to both methods. It is also expected behavior that an existing contact that has not yet confirmed their subscription can have their contact fields updated through the /sign_up_form endpoint. If Confirm Opt-In is enabled on an account, that contact can’t be sent campaigns until their subscription is confirmed.
Please have a look and let us know if you have any other questions!
Regards,
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