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Troubleshooting reference

Find the symptom, read the likely causes in order of probability, apply the fix. Covers the builder, the build and the app on the phone.

8 min read·4 sections·updated Sep 2026
TL;DR

Blank screen: a root-relative path or a history-mode router. Missing images: letter case or CSS url() relative to the stylesheet. Unstyled offline: CDN files. Won't install over the old version: package name, signing key or versionCode.

In the builder

Message or symptomCauseFix
"That ZIP couldn't be opened"Not a standard ZIP (RAR/7z renamed, corrupted, password-protected)Re-create it with your system's Compress / "Send to → Compressed folder"
"That ZIP is empty"Only folders or only __MACOSX entriesZip the files inside the folder
"No HTML page was found"No .html file anywhereAdd index.html; for frameworks, zip the build output
Size limit messageOver 5 MB (free) / 18 MB (Pro) zippedTreemap → compress images → remove junk
Preview opens the wrong pageSeveral candidate pages; the shallowest HTML file wonPut the real index.html at the root — root flattener
Content rejectedPage text matched a restricted categoryReview the flagged content; contact support if it is a false positive

The app shows a blank or broken screen

SymptomLikely causeFix
Completely blank white screenMain script requested from /assets/… (root path) → 404Relative base (base: './' etc.) — configurator
Blank, or your 404 route, but assets loadHistory-mode router sees /web/index.htmlHash routing
Page works, then blank after pull-to-refreshReloading a history-mode deep URLHash routing, or turn off pull-to-refresh
Blank on old phones onlyJS syntax newer than the WebViewFeature checker; lower the build target
Unstyled pageStylesheet path wrong, wrong case, or from a CDN while offlineCase checker, CDN localizer
Some images missingLetter case, or CSS url() resolved from the stylesheet's folderCase checker; url(../img/x.webp)
Tiny, zoomed-out pageNo viewport meta tag<meta name="viewport" content="width=device-width, initial-scale=1">
Link to folder/ shows an errorDirectory URLs are not expanded to index.htmlLink to folder/index.html

Runtime features

SymptomLikely causeFix
API calls fail, work on the websiteCORS does not allow https://appassets.androidplatform.netAllow the origin
Logged out on every requestSameSite=Lax session cookie not sent cross-siteBearer token auth
Google sign-in error disallowed_useragentGoogle blocks OAuth in WebViewsEmail/password, email link or phone sign-in
Camera / location does nothingPermission not switched on, or denied by the userPermissions step (Pro); handle the error callback
Share button throwsnavigator.share is undefined in WebViewFeature-detect; copy-link fallback
Download / export button does nothingNo download manager in the appWorkarounds
tel: / mailto: shows an error pageFree build loads them in the WebViewPro hands them to the phone's apps
Service worker errors in the consoleRegistration is not supported for bundled filesGuard it with the hostname check

Install and update

MessageCauseFix
"App not installed" / "package conflicts with an existing package"Same package name, different signing keyUninstall the old app (data is lost) or sign with the original key
Update refused, older version already installedNew versionCode is not higherIncrease the version and rebuild
"For your security, your phone is not allowed to install unknown apps"Sideloading not yet allowed for that browser/file managerTap Settings in the prompt and allow it once
"Blocked by Play Protect"An unfamiliar developer signature"More details → Install anyway"; publishing through Play removes the prompt for users
"There was a problem parsing the package"Download incomplete, or file is an AABRe-download; install the APK, not the AAB

FAQ

My problem is not listed — where do I start?

Reproduce the app on your computer by serving the build under /web/ (see the debugging doc) and read the first error in the console. It is almost always a path, a route or a network dependency.

Can support look at my ZIP?

Yes — send it through the contact page with the symptom and the phone model. Remove any secrets first; you should anyway, since they would ship in the APK.

Tools for this step

Unzip it on a phone today

Upload the ZIP, name the app, pick an icon — and download a signed APK a few minutes later. Free builds, no watermark, no Android Studio.

Convert a ZIP — free site.zip → app-release.apk