Springboot and React application not redirecting

Question

I have a Springboot and React app with a ForwardingController:

@Controller
public class ForwardingController {

    @RequestMapping(value = {"", "/", "/{path:[^\\.]+}/**"})
    public String index(Model model) {
        return "forward:/index.html";
    }
}

// The regex is copied from another StackOverflow post

When I curl http://localhost:8085/tool I get an empty response.

In the browser I get a "site cannot be reached" page.

When I curl http://localhost:8085/tool/ I am forwarded to the index page.

If I send someone any of the following links and they click on one, they also land on a "site cannot be reached" page.

http://localhost:8085/tool

http://localhost:8085/tool/

http://localhost:8085/tool/dashboard

What do I need to change to resolve this?

(The tool is hosted - the links I provided are for debugging locally)

I don't think this is a client-side issue but here is my React route:

<React.Fragment>
    <BrowserRouter>
        <Route path="/tool" render={(props) => <MainLayout {...props} />} />
        <Redirect from="/" to="/tool/dashboard" />
    </BrowserRouter>
</React.Fragment>