Direct links' limits?

I have a small autoupdating application (lesser than a few MB), and as I don't have a personal server yet I use dropbox as a storage for updates (all purposes are educational). The app requires direct links to a .txt file and a .zip with an update - it works with dropbox perfectly.
However, after doing that in the past it led to direct links being blocked on any file stored on the particular account - not just expiring, but new ones were not accessible by the application either.

Thus a question: what are the de-facto limits of the Dropbox API for being accessed that way? Number of requests, size of files? Wherever I searched, there does not seem to be any concrete info yet Dropbox certainly has a feature to stop the direct links overuse.