I was able to make it work by importing the feature type definition from an existing CSV with spaces in the column names.

Thanks for the quick response. I'm not really sure how to implement that solution, but I'll try it.

You could also just choose not to write the field names in the writer, and send a record which contains the field names including spaces as the first record to write.

Thanks to all for your help. Turns out I was making a simple mistake, which resulted in a problem that should not have been a problem. It is simple to add the white space in the writer itself by using the "Manual" radio button under the "User Attributes" tab. When I did that, I inadvertently forgot to update the "Value" field on the right-hand side to the pane to correspond with the correct source field, which at this point does not automatically match due to adding the white space manually.