I have created a custom logical unit and within it a custom enumeration field. I want to be able to select the LOV button when clicking on this field, however it is greyed out. If this is not possible, I would like to customise the options on shown on this custom field based on the WO SITE value selected in the header of the Service Quotation.

I have ticked the List of Values option as below, updated page layout and reloaded configuration however nothing seems to work.