Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You asked for a random id with a length that rush cannot make. Let's see the rule. Id dot random draws n characters at random, from an alphabet. The length n must be a whole number, and it must be between one and four thousand ninety-six. Zero characters would be an empty id, which identifies nothing. A fraction of a character does not exist. A negative number makes no sense. And a number above four thousand ninety-six is far beyond any id you could need, so it is more likely a mistake, like a unit mix-up, than a plan. Rush refuses and names the length you gave in the first slot, and the second slot explains what is wrong. Most real ids are short. Sixteen or twenty-four characters from a decent alphabet is already more than enough to make collisions practically impossible. Pick a whole number in the range, and you will get your id.
Text from the Rush engine's error catalogue.