Just for clarity could you confirm that when you replaced www.dropbox.com
with dl.dropboxusercontent.com and deleted "?raw=1" then the existing
code worked?For me I got an error message because the Download did not conform to category etc structure. The revised code is to avoid the error message when it is an external file. But it seems that you do not get that message with the original code.
This suggests that I have a different setup to yours. I can then compare your cofiguration setup with mine. Alternatively if you are able to access your database could you export jD table <prefix>_jdownloads_config as a csv file, put it in a zip and send to me by PM please.
If you do not have that access then use jD Tools - Backup to create a jD Database backup and send the file, also as a zip, to me by PM.