I can confirm that the url indeed does not work in the radio. (Edit: It is fixed now.)

Dropbox might block the user agent of the radio (run by the bass.dll of the game) which can not be changed by this addon. The radio is a client that can not change the behavour of the server. That's why it works in the browser, but not in the radio.

However it could also be the file name. Just to be sure, can you test a file with a file name that does not contain any whitespace characters (use just letters and numbers) for me?

I replaced the link with one with no white spaces.
here is the link, still doesn't work.
https://www.dropbox.com/s/424s0m77e25npj4/Worldwide.mp3?dl=1

(Tried both on a server and on a singleplayer)

Unfortunately I have bad news for you then. Dropbox does not support the user agent the radio identifies it self with. This can not be fixed by an addon update.

Any other methods I can use to put music into the radio then?

Upload load it to a file hoster that allows hot linking and put the direct url to the file. I can not do any recommendations on good providers, though. Self hosting the file is an option too, but that is only practical if you are comfortable with the server administration topic.

The radio works best with radio streams, so that's my most recommended use case.

I did some testing and I found out that there is something I can do about. That will cause some other quirks as songs not being sync/seekable, but that probably is the lesser bad. We gonna see a patch soon!

Thank you so much!

Ok, the update is done. Dropbox should work quite reliably now. We got lucky with this one. Dropbox does not block request from the radio, so far I can tell. It was just some URL issues. The radio auto-converts Dropbox URLs, so the user doesn't have to.

The cache of the radio works better too, so the radio will no longer hammer the download server with requests once it got the files.

I can accually recommended Dropbox now!

Can you confirm that it works on your end for me? Btw. I also found out that your file ("Mr. Worldwide") might be broken (cut off, during download?).

Works on my side. Great Work.

This Addon definitely gets my recommendation.

Thanks. :)

Closed as solved.