Error message received from Http Server, Code 429: too_many_write_operations/...; Caused by: Error m

The 'too_many_write_operations' error indicates "lock contention". That's a result of how Dropbox works on the backend. This is a technical inability to make a modification in the account or shared folder at the time of the API call. This error indicates that there was simultaneous activity in the account, shared folder, or app folder preventing your app from making the state-modifying call (e.g., adding, editing, moving, or deleting files) it is attempting. The simultaneous activity could be coming from your app itself, or elsewhere, e.g., from the user's desktop client. It can come from the same user, or another member of a shared folder. You can find more information about lock contention here: 

https://www.dropbox.com/developers/reference/data-ingress-guide

In short, to avoid this error, you should avoid making multiple concurrent state modifications. E.g., don't issue multiple such requests at a time, and use batch endpoints whenever possible. That won't guarantee that you won't run in to this error though, as contention can still come from other sources, so you may also want to implement automatic retries in your app

The 'path/conflict/file' error indicates that the file couldn't be uploaded because there's already a file at the specified path. You can control what happens in this case using the 'mode' and 'autorename' parameters. You can find more information on this in the upload documentation.