From the docs: "If the app does not respond with 2XX, then the server should try again later." "Shirley has her client in maintenence mode; jerrold.me will at

From the docs: "If the app does not respond with 2XX, then the server should try again later." "Shirley has her client in maintenence mode; jerrold.me will attempt to deliver the notification later using an exponential backoff algorithm."