Several weeks ago, Dropbox disabled access to all apps using v1 of their integration API. Unfortunately, I never received noticed that they were deprecating support for that version of the API, so the loss of connection to Dropbox came as a surprise.
We are in the process of creating an update to the Pro and Amazon Underground versions of the app and implementing a new API for Dropbox capability, and this same API will allow us to easily add other cloud-based storage solutions for access (Google Drive, Microsoft OneDrive, etc). We are in early Alpha testing on the update, and will be releasing a Beta soon for larger-scale testing.
Thanks for your understanding on the issue, hopefully we’ll have the new integration sorted and released soon to everyone.