Firebase - Handle cloud events within NestJS Framework

Turns out I was very close to the solution. instead of getService, I had to use get, like so:

const bootstrap = async (expressInstance: Express) => {
  const app = await NestFactory.create(AppModule, expressInstance);
  await app.init();

  return app;
};

const main = bootstrap(server);

export const subscriptions = functions
  .pubsub
  .topic('cron-topic')
  .onPublish((context, message) => main.then(app => {
    return app.get(SubscribeService).initDailyCharges(context, message));
  });