I'm trying to join a shapefile with an Excel file I converted into a CSV. I had done this before with the same shapefile but with a different CSV but this time when I try to select the column it's removed from the join list. I have tried exporting the CSV as DBF then turning it back into a CSV as well which did not work. I have included two screenshots below. I want to use the column PCODE3 because it shares the same data as MUN_P_6. Screenshots:
Full list of fields:
Limited list of fields: