Ok, so this is what Dropbox support says about the zip file is too large. Please add it to your dropbox error:
At this time, it isn’t possible for anyone – whether they’re a Dropbox user or not – to download zip files from a shared link that are larger than 1 GB.
If people you send a link to (who don’t have Dropbox accounts) need to download a folder of this size we recommend that they either download the file in smaller parts or start a Dropbox account. Doing the latter would allow them to download the Dropbox desktop application, and doing that would enable them to choose the “Add to my Dropbox” option. Using this option would allow the files you shared to be synced to their computer
Other symptoms of the zip file being too large might be that Dropbox doesn’t respond when you try to download, or it may show error 400. This will depend on which browser you’re using.
Another workaround (that I’m looking at) is just to hire a Microsoft Azure VM, install WordPress and attach downloads to a password protected blog. You’d need to maintain the blog (update it regularly), find a plugin that secures the download and make the download directory not browsable (and hidden from search engines).
This solution will cost about $200-$300 instead of $75 from Dropbox, but it will allow you to share links with users that can be larger. Another advantage of this is that it has the power of a blog and will save you money if you have a larger Dropbox user base.