How to properly inactivate a Business Partner via DI API?

I need to inactivate thousands of abandoned Leads. I'm doing it by loading up each one, setting Valid = NO, and saving it back to the database. Here is my code:

var ocrd = Company.GetBusinessObject( SAPbobsCOM.BoObjectTypes.oBusinessPartners ) as SAPbobsCOM.BusinessPartners;

foreach ( var cardCode in abandonedLeadList ) {
  if ( ocrd.GetByKey( cardCode ) ) {
    ocrd.Valid = SAPbobsCOM.BoYesNoEnum.tNO;
    if ( ocrd.Update() != 0 ) {
      // Code here to keep a list of the ones we could not write, along with error codes and messages
    }
  }
}

The intent of this change is to inactivate the record by setting its validFor flag to 'N'.

I have stepped through this code when debugging. The call to ocrd.Update() returns 0, indicating success, and in the database, the record's UpdateDate and UpdateTS indicate a save happens -- but the validFor flag remains 'Y' after the update, and the Lead remains active.

What am I missing? What is the proper way to inactivate a Business Partner programmatically?

My SAP version is Business One 9.3 (9.30.180) PL:08 (64-bit)

To make a Business Partner inactive use the Frozen Property via the DI-API along with the Valid Property:

        ocrd.Valid = SAPbobsCOM.BoYesNoEnum.tNO
        ocrd.Frozen = SAPbobsCOM.BoYesNoEnum.tYES