Xamarin forms - custom login via PKCE

I am developing a native mobile app using Xamarin forms and as per the suggested flow, I would like to implement “Authorization Code Grant Flow with PKCE”.
To use the API I need to provide a callback URI.
What I dont understand is when I am making this call from the client app, how to give a server side URL.
there is requirement of giving a URL that Auth0 redirects with the authorization.
So the question is, I do not want to have a browser opening up when using the API and also how can once specify a web url on the native app.
I am confused.
I am a newbie to Auth0, please guide.

As you’ll notice, for example, in the Xamarin quickstart even though you are required to provide a callback URL (this requirement is intrinsic to the underlying authentication protocol), the callback URL in the case of a native application may not need to be a valid HTTPS URL associated with a web application.

The quickstart I linked to uses a custom URI scheme that is not associated with an underlying server side web application. The URL is only used so that your native application can be aware that the authentication response was delivered. If you haven’t done so already, you should follow a native quickstart.