Unable to access a list in a different farm using client context(csom). the remote server returned an error: (401) unauthorized.

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SharePoint

I am trying to access a list in a site collection of different farm using CSOM. But I am getting the error "The remote server returned an error: (401) Unauthorized." Code I used is below.

using (ClientContext ctx = new ClientContext(URL))
{
Web web = ctx.Site.RootWeb;
ctx.Load(web);
ctx.ExecuteQuery();
Console.Write(web.Title);
}

Always getting the authentication error. Is any special confoguration required between farms? Please help. Thanks in advance.

What I have tried:

I tried these steps

ctx.Credentials = CredentialCache.DefaultNetworkCredentials;

ctx.Credentials = new NetworkCredential("username", "password", "domain");

But no use. Still getting the same error. Anything to change in web.config or anywhere? I tried using NTLM webapps and kerbos authentications. No difference.