Billing: only if needed, and by you
Cloud Functions (Firebase Blaze plan) and Google Maps need a billing account; everything else in this guide works without one. If Fodide says the app needs one, open Billing → My projects, the project's ⋮ → Change billing, choose or create your billing account, Set account. Set a budget alert there too.
Fodide never links billing. Blaze still includes the free amounts (for example 2 million function calls a month).