import Courier from '@trycourier/courier';

const client = new Courier({
  apiKey: process.env['COURIER_API_KEY'], // This is the default and can be omitted
});

const response = await client.profiles.lists.subscribe('user_id', {
  lists: [{ listId: 'listId' }],
});

console.log(response.status);

{
  "status": "SUCCESS"
}