Funnily enough, I have just encountered the same issue again! I ended up going with the embed option to solve this originally.
What I am thinking is that I need to make an api call to this endpoint in order to actually get a dropbox image or file link that plays nice with apis. As i understand it, the dropbox share links are not a link to the actual file, but a preview.
Edit: this is not a solution as of yet, just an idea
Oh sorry mate. I was talking about image, but the file is another thing I need to sort too!
I notice you have the data as a url for the source file. I think it needs to be data / binary. So you need a download dropbox file step prior to the create new webflow item. I couldn’t get this to work, but Webflow support could at the time…
With regard to the embed, that was done with Google drive. Not sure you can embed with dropbox files. Worst case is you link off page to the original dropbox share url.
Note a common issue is Webflow form settings should not require user to be logged in.
Use a Webflow api module as opposed to the Webflow integromat create items modules. The standard module reveals the source file name and data dialog as you have posted above and this does not work. It needs a “your file field name”: “public url” structure to work. Hope this helps.