When a GitHub build fails

Open the failed run on GitHub (the arrow next to it) and read the failing step. These are the ones seen in practice:

Message	Cause and fix
Preflight: still the placeholder	The app's URL was never set to your real published address. Publish the site, then rebuild.
Preflight: returned 404	Nothing is published at that address yet.
Invalid PNG signature	The logo file is not a real image. Regenerate it in the Brand tab. Newer builds repair this automatically.
SecKeychainItemImport failed	An empty Apple certificate secret. Either set all the signing secrets or none.
invalid source release: 21	Java version mismatch — the workflow pins Java 21 for a reason; do not lower it.
Could not find method kotlinOptions()	Something edited android/app/build.gradle. Never patch it; the platform's workflow does not need to.

Artifacts expire

GitHub deletes build files after a retention window. If a download says the artifact expired, run the build again — nothing is wrong.

The workflow is managed for you

Every build refreshes the workflow file from the platform before dispatching, so hand edits to it are replaced. This is deliberate: the pinned tool versions in it were each earned by debugging a real failure.