Add a subscriber from your own form

To add a contact to a list from your own website form, POST to the list subscribe endpoint with a bearer token:

POST /api/v1/lists/{listId}/subscribe
Authorization: Bearer <your key>
Content-Type: application/json

{ "email": "person@example.com", "first_name": "Sam" }

If the list has double opt-in enabled, the contact gets a confirmation email and is not active until they click. The endpoint is idempotent: posting the same email twice updates rather than duplicates.