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.
Constant Contact provides developers with free access to our API endpoints so that you can build your own application for integration. If you are developing your own integration/plugin, you can get started below:
Getting Started with V3 API
If you are looking to connect an existing or pre-built integration with your CMS, you may need to contact that service’s support for assistance. If you are able to let us know the name of the CMS you are using, we’d be happy to take a look and see if we can provide more insight.
You can also search for pre-built integrations in the Integrations Tab of your account, or search for Apps, Integrations, and Services via Constant Contact’s marketplace:
Integrations Tab (must be logged into account)
Constant Contact Marketplace
Please have a look and let us know if you have any other questions!