On my Mac, through the Dropbox app, I turned on selective syncing to save space on my hard drive, which was at max capacity and not allowing Dropbox to sync because it was so full. Now I cannot attach or open any documents from Dropbox on my computer. For example, I have no way of attaching documents to emails, or opening them in Adobe, Excel, or Word. I tried turning on Smart Syncing, which did nothing. I cannot open up the desktop app anymore, as now when I click on the application, it opens up my empty Dropbox in the Finder app. This issue has put my work at a standstill and I cannot do anything to undo the changes to the settings. I really need help. Thank you.
Selective sync completely removes the folders from your Dropbox folder, so it would make sense if you weren't able to access your files, attach documents to emails, etc.
You'll need to sync them back to your computer, through the selective sync settings. They will sync as 'online-only' files, which won't take up space on your hard drive and you will be able to access them again.