API Copy/Sync two folders in dropbox account

I recommend reading the "Detecting Changes Guide" here:

https://www.dropbox.com/lp/developers/reference/detecting-changes-guide

That covers the options for efficiently detecting and listing just the changes that have occurred since you last checked, e.g., using the "cursor" functionality on /2/files/list_folder[/continue]. For cases where you can't just copy the folder in its entirety, you could use that to determine what specific items need to be copied.

Also, for the actual copying, when you have multiple items to copy, you can use the /2/files/copy_batch_v2 endpoint to do so in bulk:

https://www.dropbox.com/developers/documentation/http/documentation#files-copy_batch