Pipelines to import csv file not working

It sounds like Dropbox may need some sort of authentication in order to grab that file which makes sense. It is protecting your account from unauthorized access. When you login via the browser it knows you and knows you can access it, when you go to the same URL with a webhook it does not know you and denies that.

I believe there is a dropbox channel in Pipelines, mine is not turned on though. You would probably need to use that to authenticate and then find the csv you want and do something else to take the csv and import it. 

Another option here is to not use Pipelines and instead use the Quickbase Sync for CSV and use Dropbox. That syncs a csv with a table. That should be much easier assuming you just want to import that csv file. Not sure on the limitations there though, a Pipeline might get you more of what you want.

https://help.quickbase.com/user-assistance/Connecting_to_a_folder_of_csv_files.html