Why is my lookup with a single column not working?

[Log_wrangler]

I have a CSV of filenames.

The column header name in the CSV is indicator_F. Index=main has a field = file, which are filenames.
I want to match indicator_F values to file values.

Here is my query ...

index=main |lookup file_hits.csv indicator_F AS file | table file indicator_F

But I keep getting errors...

Error in 'lookup' command: All of the fields in the lookup table are specified as lookups, leaving no destination fields.

Not sure what I am doing wrong here...

Please advise.

Thank you!

[Log_wrangler · Accepted solution]

added a column in front of the other, and it works... IDK why but it does.