EF Core many-to-many relation error

    public class Student
    {
        public Guid Id { get; set; }

        public User User { get; set; }

        [SwaggerIgnore]
        public int StudentNumber { get; set; }

        [JsonIgnore]
        public ICollection<Class>? Classes { get; set; }
        [JsonIgnore]
        public List<ClassStudent> ClassStudents { get; set; }
    }

    public class Class
    {
        public Guid Id { get; set; }

        public string ClassName { get; set; }

        public string ClassRoom { get; set; }

        [SwaggerIgnore]
        public ICollection<Student>? Students { get; set; }
        [JsonIgnore]
        public List<ClassStudent> ClassStudents { get; set; }

        public Guid TeacherForeignKey { get; set; }

        [JsonIgnore]
        public Teacher? Teacher { get; set; }
    }

    public class ClassStudent
    {
        public DateTime StartDate { get; set; }

        public Guid ClassId { get; set; }
        public Class Class { get; set; }

        public Guid StudentId { get; set; }
        public Student Student { get; set; }
    }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Class>()
                .HasOne(p => p.Teacher)
                .WithMany(x => x.Classes)
                .HasForeignKey(x => x.TeacherForeignKey);

            modelBuilder.Entity<Class>()
                .HasMany(x => x.Students)
                .WithMany(x => x.Classes)
                .UsingEntity<ClassStudent>(
                    x => x.HasOne(x => x.Student).WithMany(x => x.ClassStudents).HasForeignKey(x => x.StudentId),
                    x => x.HasOne(x => x.Class).WithMany(x => x.ClassStudents).HasForeignKey(x => x.ClassId),
                    x =>
                    {
                        x.Property(pt => pt.StartDate).HasDefaultValueSql("CURRENT_TIMESTAMP");
                        x.HasKey(x => new { x.ClassId, x.StudentId });
                    }
                );

            modelBuilder.Entity<Student>().Property(x => x.StudentNumber).ValueGeneratedOnAdd();
        }