import Courier from '@trycourier/courier';

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

await client.lists.subscriptions.subscribe('list_id', { recipients: [{ recipientId: 'recipientId' }] });

{
  "message": "<string>",
  "type": "invalid_request_error"
}