Why same code work differently? "Render HTML Elements to the DOM"

[Plabon_Kumer_Sarker]

Here is the problem, Render HTML Elements to the DOM.
When I run this,

ReactDOM.render(JSX,document.getElementById("Challenge-node"));

It’s not working it says,

Build error, open your browser console to learn more.

But When I run this,

ReactDOM.render(JSX,
               document.getElementById("challenge-node"));

It’s working properly!

Why same code work differently?

[sanity]

There’s capitalization error in the id in first code.

[Plabon_Kumer_Sarker]

I feel shy