Error while copying content to a stream in C#

Rephoto If you wish to optimize your upload process, please refer to the Performance Guide: https://developers.dropbox.com/dbx-performance-guide

That offers some ways you may be able to improve your effective overall upload speed. For example, there are batching and parallelization features you can use.

For instance, as Здравко noted, the default upload session type is "sequential", but you can use "concurrent" to upload file pieces in parallel. That would require you to make some more changes to your code to properly send those pieces in parallel though.