Hey @AdminTest03 - sorry to jump in, but I just wanted to mention that if Dropbox Sign for Salesforce is installed in your production environment it will also be installed in any sandbox environments created post installation.
Within a sandbox in the Dropbox Sign App Settings page a prompt to connect is displayed. Use the same Dropbox Sign login credentials when connecting to a sandbox as those used in production.
For more information, you can have a look here.