search.lookup options

Hello everyone,

I am trying to retrieve conversion rate from Units Type but getting the following error:

Any idea what the issue could be?

Thanks :)

The script is as below:

function validateLine(scriptContext) {

    var currentRecord = scriptContext.currentRecord;

   var sublistName = scriptContext.sublistId;

  var sublistFieldName = scriptContext.fieldId;

  var sublistName = 'item';

  var sublistFieldName = 'units';

   

   if(sublistName === 'item' && sublistFieldName === 'units'){

  var soUnits = currentRecord.getCurrentSublistValue({

             sublistId: 'item',

             fieldId: 'units',

               });

        

        var fieldLookUp = search.lookupFields({

      type: search.Type.UNITS_TYPE,

      id: soUnits,

      columns: ['conversionrate']

     });

        var Con_Rate= fieldLookUp.conversionrate[0].value

         

         

        var SoQuantity = currentRecord.getCurrentSublistValue({

             sublistId: 'item',

             fieldId: 'quantity',

               });

        

        

        var totalPacks = SoQuantity*soUnits

        

        currentRecord.setCurrentSublistValue({

             sublistId: 'item',

             fieldId: 'custcol13',