X_OUTBOUND_RETRY_UNSAFE
Means
a retry was asked for on a write that is not idempotent
Typical cause
outbound() was given retry on a POST or PATCH without idempotent: true. A replayed write is a second charge, so the call is refused before anything is sent
Fix
add idempotent: true to the outbound() call with the vendor's idempotency-key header, or drop retry