Adding a server side page to a Blazor project

I'm trying to add a new page to a Blazor project.

So I add the new .razor file in the Components/Pages folder of the server side project and add a @page directive to the top of it.

@page "/OtherPage"<h3>OtherPage</h3>@code {}<p>This is the other page.</p>

When I navigate to /OtherPage the page appears but then disappears and says Not found.

What is wrong?