Data Table: Join - how do I name the column names?

I am trying to join two tables and I cannot name the columns correctly. I have checked the underlying CSV files to ensure that the column headings are correct and matched my Action specifications accordingly, but I still get a bot error stating:

""Cannot find column with name [insert col name here]" in data table. Please check whether the column name is valid. If the problem persists""

Am I missing something?

I first read a CSV to a table variable. The CSV has headers. Then I join that table to another table with the same situation.

I think I am just missing something that is implicitly understood about the way A360 wants me to do this.

Any help is appreciated!