default organization doesn't exist

I am trying to register the client on Satellite 6 after I unregistered it previously. I am using the following command, however, I am getting error Organization Default_Organization does not exist. I ran hammer organization list on my Sat 6 and I can see the following there.
hammer organization list

1 Default Organization Default_Organization Repo View Cert

subscription-manager register --org=Default_Organization --activationkey=1-test-key-1