I've just downloaded CloudPack for Firemonkey 22.214.171.124 for 10 Seattle and it will no longer auth.
When I put my valid App Key and Secret in the Cloud Storage demo app and try to DoAuth() it shows a page saying "the request to link the app is invalid".
The keys are correct and used to work before the update.
Internally I've also noticed that you've switched from OAuth v1 to v2 so wonder if that's causing problems too? I've registered the Callback URL with my app in the Dropbox app console so should be ok too.
Am I doing something wrong or is there something extra I need to add in the new version to make this work?