XLOOKUP columns

SergeiBaklan I understand that XLOOKUP is a formula in Excel used for pulling together related information. Now I am taking a course in LinkedIn and in this part I am learning about formulas and XLOOKUP which is one the most used formulas replacing VLOOKUP and HLOOKUP. In the tutorial, the teacher is using an example: associating employee ID-numbers (column G) with employee names (column H). He shows how to add a whole column containing names into the function. For this he writes "=xlookup(" and then to add the desired value which is the ID# he wants to match with an employee he clicks in the cell where the ID# resides. This makes the formula looking like "=xlookup(G2" after which he adds a comma. Then he looks for the lookup array and in this case the ID# are in a column called C. To add the whole column into the formula he clicks on the C which is the name of that column. When ge does this the formula looks like "=xlookup(G2,C:C". Now, when I click on C I get a pop up message instead reading "There is a problem with the formula. Not trying to type a formula? ..." going on explaining what to do if you are not typing a formula, which I am. So for some reason Excel 365 for Mac does not acknowledge my typing on the column C as part of writing a formula. Why is that? 

Thanks in advance!