where are you stuck in?

Hmm, I think I stuck in finding attack vector, like when I look at other problems: they allow me to input in some way to manipulate the flow of the application. But in this problem: I can't find any attack vector or "input" that I can send my payload to? I try to learn a lot about nextjs but the best thing I can find is: call the API getFlag() directly https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions-and-mutations#security if knowing its ID.