Error: Object "seat1" Not Found

Hello, I am new to learning R (mostly through datacamp) and it appears the dataset I'm trying to work with is loaded correctly. It is a .csv file with variable names as the columns and data for each participant in each row. Each column is an item from a scale (e.g. SEAT1-SEAT24, RSE1-RSE10). I'm a psychologist and created a scale with my psych testing class in the spring. I'm also much more used to programs like SPSS, JASP, and JAMOVI, so this has been challenging.

I'll try to include screen capture, but the data set looks like this....

SEAT1 SEAT2 SEAT3
5 7 1
2 6 5

I attempted to sum the SEAT items by entering (for example)

sum(SEAT1, SEAT2, SEAT3)

and I get back an error stating that the object 'seat1' is not found. When I call up variable names it lists all of the 60 columns for the different variables I have. So its all in there.

I'm sure I'm missing something and appreciate any thoughts you may have. Thank you!!