vercel.json specifies that /api/bitmap/wikipedia.bmp should run every 5 minutes. However, on the Hobby plan, Vercel only allows one cron trigger per day.
I'm not sure if compatibility with the Hobby plan is a priority for this project, but it would probably get more people adopting it.
This is hard to debug because Vercel deployment fails with no error message, only a link to the pricing page to hint at what the problem is.