Hello MKTG_Team,
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.
After reviewing the logs for your keys, I found that the grant_type value being used in your token requests is “client_credentials”. If you are trying to use the authorization code flow, the required grant_type is “authorization_code”.
Our access tokens expire after 1440 minutes (86,400 seconds) but your application can utilize refresh tokens to extend the lifespan of an access token by exchanging it for a new set of access and refresh tokens. For more information on this process I am including overview documentation for our OAuth2 authentication and the Authorization Code flow below.
OAuth2 Overview:
https://developer.constantcontact.com/api_guide/auth_overview.html
Authorization Code Flow:
https://developer.constantcontact.com/api_guide/server_flow.html
Please have a look and let us know if you have any other questions!
Regards,
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