Upload your files in the builder
Build a demo APK first to try it on your phone; Builder Pro builds the full app and the AAB.
Build for files, not a server
Inside the app there is no web server, so the build must use relative paths. In Vite set base: './'; in Create React App set "homepage": "."; in Vue CLI set publicPath: './'. Then build and ZIP the output folder.
Routing
History-mode routes like /settings need a server to rewrite them to index.html. Switch to hash routing (createHashRouter in React Router, createWebHashHistory in Vue Router) and every route works offline.
Upload and build
Open the builder in HTML/ZIP mode, upload the ZIP and check the preview. If you see a blank page, the cause is almost always an absolute path — see ZIP to APK.
Prefer a live deploy?
If your app is already deployed (Vercel, Netlify, Cloudflare Pages), you can paste its URL instead and build a website app. Updates then ship with each deploy, at the cost of needing a connection.