Configurator Designer- How to use Dynamic Attribute ( property on an Input )?

In the configurator designer, when I inspect a control, the last bold heading is ‘Dynamic Attribute’. It has a field for “Dynamic Attribute ID” but I am unable to enter any text there.
Also, it seems I would have to specify the Dynamic Attribute Class ID before I can specify the Dynamic Attribute ID but there is only the single id field.

I found the “Configurator Management > Setup > Dynamic Attribute Class” section where I created one Dynamic Attribute Class with two Dynamic Attribute children- both checkbox fields.
It defaulted to Schema Name: ‘Erp’ and Table Name ‘Part’ which may not be correct for the configurator designer.( I believe it uses UD01 and UD09 ?)

The docs were not much help explaining how this feature is supposed to work or how to get it working. They said that 'External Ref" must be set to True but it defaults False and the whole section is grayed out.