Hi,
What are you trying to protect?
If you are trying to protect enterprise apps like SQL or Oracle, or VMware, then the SnapCenter Standard license is applied at the controller level using the SnapManagerSuite license.
In this scenario you need to add the SVM and not the cluster into SnapCenter.
The cluster context is ONLY used for the Advanced use cases. This is currently limited to the NAS File Services capability.
In this case there is some advacned automation that requires the cluster context and only the cluster is used.
Hope this helps,
John