I had an 404 error for a test web app that used a NGINX reverse-proxy config file, which was pretty hard to track it down. Most of the routes worked fine, except pages under an /admin folder, all throwing 404 error, page not found.
The easiest thing to track it down is a break-point somewhere, but where exactly, for a page that's not found? So, I added temporarily a middleware in Startup.cs, by the book:
app.Use(async (context, next) =>
{
// Do work that doesn't write to the Response.
await next.Invoke();
// Do logging or other work that doesn't write to the Response.
});
Then just add the break-point on highlighted line and inspect the Request object.
In my case I only needed a backslash in proxy_pass parameter of NGINX's config file.
