After doing all the steps you indicated here --> https://blogs.dropbox.com/developers/2015/05/try-out-swiftydropbox-the-new-swift-sdk-for-dropbox-api-v2/
I could logged in a client successfully but then if I want for example to retrieve user's data with client.usersGetCurrentAccount function, I always got the same error:
Bad Input: Error in call to API function "users/get_current_account": Your app is not currently allowed to use the API v2 beta API.