There is a last check we can do.

If it worked, we receive a response with HTTP code 200.
If there is any failure, the server can send a 500 (e.g. if RabbitMQ is down).

The reqwest response offers a status method to check if the code is 200/201/204:

if !res.status().is_success() {
   eprintln!("The notifications server can't process the notification.");
   exit(2); // Let's use another code so a script can know at what step it failed.
}

We aren't especially interested by the specifics, as the notifications center also logged the error in its own log, and there is nothing the push script or the user using it can do.