# X_PWA_SYNC_FLUSH_FAILED

## Means

the background-sync outbox flush was rejected

## Typical cause

**registered, thrown by nothing since 21.0.0.** Until then the worker POSTed `/_x/outbox/flush`, a route nothing mounted, and raised this on a non-2xx. The worker now posts `OUTBOX_DRAIN_MESSAGE` to open tabs, and realtime's outbox replays over HTTP

## Fix

delete any branch that matches this code, because it never runs. An app still generating the old worker: delete `backgroundSync: { flushEndpoint }` from its `generateServiceWorker` call

[PWA and build skew](/error-codes#pwa-and-build-skew)