Add Numbering Sequence to Custom CD Field in Custom Screen

Hi I am trying to add numbering sequence logic to the below custom screen, but get Container ID cannot be empty error when trying to save the record.

 #region ContainerCD
    [PXDBString(25,  IsUnicode = true, IsKey = true,
                InputMask = ">CCCCCCCCCCCCCCCCCCCCCCCCC")]
      [PXDefault]
    [PXSelector(typeof(MAINContainer.containerCD))]
      [AutoNumber(typeof(Search<PX.Objects.CS.Numbering.numberingID,
    Where<PX.Objects.CS.Numbering.numberingID, Equal<StringConstant_CONTAINERN>>>),
    typeof(AccessInfo.businessDate))]
    [PXUIField(DisplayName = "Container ID")]
    public virtual string ContainerCD { get; set; }
    public abstract class containerCD : PX.Data.BQL.BqlString.Field<containerCD> { }
    #endregion

namespace CFInnova11112025
{
  public class StringConstant_CONTAINERN : PX.Data.BQL.BqlString.Constant<StringConstant_CONTAINERN>
  {
    public StringConstant_CONTAINERN() : base("CONTAINERN") { }
  }
}

Trace: Container ID cannot be empty

Can I please know what else is required here?

Thank you!