You will need to work with your account team to acquire a license for SnapCenter.
They will need to order a $0 trial license.
As a reminder, the SnapCenter Standard capacity based license is only needed for ONTAP Cloud and ONTAP Select systems.
If you as using a FAS or AFF then you need a different license - The SnapManagerSuite trial license.
If you are already using a SnapManager product that is licenses at the controller (not the host) level, which uses the SnapManagerSuite license, then you already fully licensed for SnapCenter Standard on FAS and AFF platforms.
I too am having a license problem with 3.0. I am trying to add a new OnTap Cluster to the storage systems, I fill out the form and receive the message illustrated below. Our clusters are licensed with the premium bundle, and the documentation states no license should be required in this scenario.