spfx custom property pane – onGetErrorMessage for PropertyFieldCollectionData CustomCollectionFieldType.dropdown not working

I’m trying to validate the inputs of my PropertyFieldCollectionData using onGetErrorMessage.

It works fine for the text input (CustomCollectionFieldType.string) but for dropdown values (CustomCollectionFieldType.dropdown) nothing happens.

I could only find validation examples for the text input field online, so I’m not sure if the code is supposed to be different for each field type…

In the example below there’s no actual validation yet, it’s just to see if the code fires at all.

How can I get onGetErrorMessage to work for the dropdown menu?

   let mySelector: any = PropertyFieldCollectionData("selectorCollectionData", {
    key: "selectorCollectionData",
    label: "Configuration",
    panelHeader: "Configuration",
    manageBtnLabel: "Manage configuration",
    value: t.properties.filterCollectionData,
    fields: (
      {
        id: "value",
        title: "Value",
        type: CustomCollectionFieldType.string,
        required: true,                      
        onGetErrorMessage: (value: string, index: number, item: any) => {

        console.log(item); // logs to console on every update
          return '';
        }
        
      },
      {            
        id: "valueType",
        title: "Value type",
        type: CustomCollectionFieldType.dropdown,
        options: (
          {
            key: "A",
            text: "A"
          },
          {
            key: "B",
            text: "B"
          },
          {
            key: "C",
            text: "C"
          }
        ),
        onGetErrorMessage: (value: string, index: number, item: any) => {

          console.log(item); // does not fire when dropdown is changed
            return '';
          }
      }
    ),
    disabled: false
  })