Listed below is the steps to send us LR catalog and Smart Previews files via Dropbox. You can also send image files (RAW or JPEG) this way.
Head on over to dropbox.com and create an account (if you don’t already have one). Once account has been made you can then create a folder: (upper right of page)
And upload the two files (lightroom catalog and {zipped} Smart Previews folder). You can drag/drop or manually add the files.
Once files have been added it should look like this:
Now to give us the Dropbox link. Go back to the home page in Drobox and hover your mouse over the folder you made:
Click on Share > Send Link
You will then be given a link to copy and paste.
That is the link you can provide in the 'Submit Images' box.
******Please note you are uploading a zipped Smart Previews folder and not the Previews folder. As they are two different folders and we can not see the image files properly if given the Previews folder.