Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You told rush you were testing on the real network, but the peer you reached is your own machine. Here is the rule. The word real, at the end of the dial command, is a claim: this run proves the protocol over a real network. Rush does not take your word for it. After connecting, it asks the kernel who the peer really is. If the answer is a loopback address, one hundred twenty-seven dot something, or colon colon one, then the traffic never left your computer, and the claim is false. Rush refuses before any handshake. Why so strict? A loopback run is a perfectly good protocol check, but it says nothing about real latency, real packet loss, or real firewalls, and presenting it as real wire would mislead everyone who reads the result. The project's rule is that real-wire claims go to the droplet, at its public address, never to localhost. The fix is simple: point the dial at the droplet, or drop the word real and call it what it is.
Text from the Rush engine's error catalogue.