UWP SQL connection Error [c#]

I try to connect to a SQL Server 2008 instance with SQL Server credentials.

With a WPF app, I have no problem.

I follow this example: https://docs.microsoft.com/en-us/windows/uwp/data-access/sql-server-databases

I have read this: How to connect to SQL server database from a Windows 10 UWP app

My connection string is:

static private string connectionString = 
     @"Data Source=SERVER\SQLSERVER;Initial Catalog=Something;
       Integrated Security=false;Persist Security Info=True;User ID=user;Password=pass";

conn = new SqlConnection(connectionString);

try
{
    conn.Open();
}
catch(Exception z)
{
    Debug.WriteLine(z.ToString());
}

I get this error

System.Data.SqlClient.SqlException (0x80131904): A connection was successfully established with the server, but then an error occurred during the login process. (provider: TCP Provider, error: 0 - L’opération a réussi)

If I try

static private string connectionString = 
    @"Data Source=SERVER\SQLSERVER;Initial Catalog = Something;
      Integrated Security=true;User ID = user;Password= pass";

I get this error

System.Data.SqlClient.SqlException (0x80131904): Failed to generate SSPI context. ErrorCode=DowngradeDetected

The same error with Integrated Security=SSPI

If someone has an idea please?

Thanks Benoit

You need to check the appropriate capabilities in your appx manifest that are required for accessing the resource on your network. Open Package.appxmanifest in VS and go to the 'Capabilities' tab.