I have a spreadsheet that has 2 columns in it that are linked to dropdown
lists. Depending on the selection made in the first column determines what is
available in the second list.

My problem is that if the user types in the vale instead of selecting it
from the list (even if what they type is correct) then my code for some
reason is not run and the next columns list will be wrong.

Is there a way that I can force the user to use the dropdown list for that
column? That is they can't simply type in the value?