Cannot retrieve data from one-to-one relationship tables in Entity Framework 6

Question

Below are the model classes. The database and tables were created properly. I can post some tested data to them through postman, but I get the Multiplicity constraint violated error when retrieving all the data from the table as shown in the picture below. In one-to-many relationship in my other applications, everything works as expected.

public class Quote
{
    public Quote()
    {
        Outlet = new Outlet();
    }
    public int Id { get; set; }
    public string RefNumber { get; set; }
    public string Status { get; set; }
    public string Name { get; set; }
    public string DeliveryAddress { get; set; }
    public DateTime DeliveryDate { get; set; }
    public string Phone { get; set; }
    public string Email { get; set; }
    public string Comment { get; set; }
    public DateTime Date { get; set; }
    public virtual Outlet Outlet { get; set; }
}

public class Outlet
{
    public Outlet()
    {
        Inlets = new List<Inlet>();
    }
    [ForeignKey("Quote")]
    public int Id { get; set; }
    public int OutletAngle { get; set; }
    public int OutletSize { get; set; }
    public string OutletType { get; set; }
    public virtual Quote Quote { get; set; }
    public ICollection<Inlet> Inlets { get; set; }

}

public class Inlet
{
    public int Id { get; set; }
    public int InletAngle { get; set; }
    public int InletSize { get; set; }
    public string InletType { get; set; }
}
}