Trying to use CONCAT formula

TRying to concatenate two fields. Using CONCAT($Last,", ",$First) and getting NAMERROR. What am I doing wrong?

Did you double-check that there are two columns named Last and First (without typo, especially about capitalization)?

Getting the column name wrong would give an AttributeError, not a NameError.

Double-click on a cell with a formula error and it should show a full error message. Click on the little grey arrow in there to expand it further and show a traceback. What do you see? Post a screenshot here if you can. For example:

Screenshot from 2023-11-04 11-59-26