Using the Letterhead API

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The Letterhead API allows you to programmatically access newsletters, audiences, metrics, and content. Two API versions are available—v2 for organization-level operations and v3 for company-level operations—both using Bearer token authentication.

API Versions

v2 (Organization-scoped)

Operates at the organization or brand level
Use for operations involving multiple companies within an organization

v3 (Company-scoped)

Operates at the individual company level
Use for company-specific operations

Authentication

All API requests require a Bearer token in the Authorization header.

Authorization: Bearer <your-api-key>

TODO: Link to managing API keys to show where to generate and retrieve your key.

Making Your First Request

Example request to list newsletters:

curl -H "Authorization: Bearer your_api_key_here" \
  https://api.letterhead.app/v3/newsletters

Replace your_api_key_here with your actual API key and adjust the endpoint URL based on which version (v2 or v3) your integration requires.

API Reference

The complete endpoint reference, including request/response formats, is auto-generated and available at:

/api/reference

Refer to that documentation for detailed endpoint specifications, parameters, and error codes.

Next Steps

Still can’t find what you need? Contact support.