4003: sending is temporarily paused: the kill-switch state is not yet loaded; retry shortly

sending is temporarily paused: the kill-switch state is not yet loaded; retry shortly. This is an HTTP 503: a dependency is unavailable right now.

• This is an operational or capability refusal, not a malformed request; the same call may succeed later.
• For a pause, honour Retry-After; for a capability refusal, send a part type the recipient’s device announced.