X_OUTBOUND_UNAVAILABLE
Means
an outbound HTTP call answered a retryable status
Typical cause
the vendor answered 5xx, 408, 409, 425 or 429 with no stated delay, on every attempt outbound() made. The vendor's fault, not the request's: meta.status names the status
Fix
curl -sS -m 5 -o /dev/null -w '%{http_code}\n' <meta.origin> — the vendor's fault: re-run the call; if meta.status persists, check the status page of the vendor meta.vendor names