Dataset Read with Schema column Invalid Syntax

I am trying to read a data-set using a column within the schema I am building. I have seen all the topics and the help and tried to put the right formula together but the formulas I have tried either return a blank or an error. I have validated that the key I want is in the data-set. Unfortunately all my column names have upper case values at the start which I think is the issue but the combinations I have tried are exhaustive some examples are below:
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, ‘ZipCode’: “ZipCode”) - returns blank
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, ZipCode:“ZipCode”) - returns blank
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, ZipCode:ZipCode) - error please use field(‘ZipCode’)
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, ZipCode:field(‘ZipCode’)) - returns blank
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, ZipCode:field(“ZipCode”)) - returns blank
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, field(“ZipCode”):field(“ZipCode”)) - Syntax error in formula

any ideas for the correct syntax?

Note I just tried the formula with a fixed key and it works correctly:
from_dataset(‘Ref_ZipCode’, ‘StateCountyCode’, ZipCode:‘33544’)