How to fix System.InvalidOperationException: Scheme already exists: Identity.Application

For example

Creating an ApplicationUser class that extends the IdentityUser class, then add a FullName property

public class ApplicationUser : IdentityUser
{
    public string FullName { get; set; }
}

Opening your Startup class, then modify your class as shown below.

services.AddIdentity<ApplicationUser, IdentityRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();