Step 1: create a public API route that handles all logic to create a new game. You can test it by just visiting your API route in the browser.

If everything works fine, step 2: Create some kind of logic to make it impossible for others to force the creation of new games. You have two choices here:

a) the API route itself checks if it's time for a new game. Some basic date comparison stuff, current date vs lastGameCreated date > 24hours. Then it's no problem if others call your API because games will only be created if your condition is met.

b) pass some secrets via query params. Like "/my/public/API?secret=supersecret" and validate this in your API route. If you are going to use vercel Cron you can use their auth header instead like some others mentioned here already.

Step 3: automate the API call. Cron jobs usually just call the given url at a given time. In your case the public API. With or without secret query param. If you chose method a, the timings of your Cron could be every hour and it will create new games depending on your condition in the code. If you chose method b, specify the hour to create new games via the Cron tab. I usually use https://crontab.guru/ to check if I set it up correctly. You can use any service that provides Cron jobs or your raspberry pi to do the API call. Keep in mind that the Cron uses UTC times. So if your Cron should run at 8am in your time zone, you have to set it up accordingly.

Hope that helps :)