Using ETL tool's REST utility to download a folder with REST get URL

For API v1, you can send these parameters as URL parameters, or form encoded in the body. For example, either of these are valid:

curl -X "POST" "https://api.dropboxapi.com/1/fileops/copy" \
 -H "Authorization: Bearer <ACCESS_TOKEN>" \
 --data "root=auto&from_path=/test.txt&to_path=/test_new.txt"

or

curl -X "POST" "https://api.dropboxapi.com/1/fileops/copy?root=auto&from_path=/test.txt&to_path=/test_new.txt" \
 -H "Authorization: Bearer <ACCESS_TOKEN>"

(Perhaps you looked at some API v2 documentation at some point? API v2 does take JSON in the body. We generally would recommend using API v2 instead of API v1, if it has all of the functionality you need anyway.)