How to check in column and if different prompt user and restrict users?

Currently, i have an column with an drop down i would like that for when user select different row if the user select in that column something not compatible it will prompt the user that this is not allow and restrict the user for adding in or typing in till they reselect the drop down, in vba

I have make an example Marco workbook where my category i have an drop down list, user are allow to select the same name however, 3G and 4D are not allow to be selected when 4D is selected, it will prompt the user that this is not allow and restrict the user for doing anything next, so how can i do this in VBA ?