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.users.preferences.updateOrCreateTopic('topic_id', {
  user_id: 'user_id',
  topic: {
    status: 'OPTED_IN',
    has_custom_routing: true,
    custom_routing: ['inbox', 'email'],
  },
});

console.log(response.message);

{
  "message": "success"
}