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 this integration, it looks like you need to generate a V2 API Key and Access Token. Below is a link to documentation on how to obtain an API Key and Access Token along with documentation on how to implement that information into the DIVI/Bloom plugin:
How to generate an API Key and Access Token: https://community.constantcontact.com/t5/Community-News/How-to-generate-an-API-Key-and-Access-Token/ba-p/293856
Connecting Constant Contact and DIVI/Bloom: https://www.elegantthemes.com/documentation/bloom/accounts/#constantcontact
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