Constant Contact V3 API

Production REST API for Constant Contact's email marketing, SMS, and events platform. OAuth2 authorization (auth code, PKCE, and JWT-bearer flows) gates all endpoints across account services, contacts, contact lists, tags, custom fields, segments, email campaigns and activities (with A/B tests, schedules, and tests), bulk activities for high-volume mutations, events (registrations, tracks, check-in, payment status), contact reporting, landing pages, and partner technology-account provisioning.