The Correct method to apply the vSAN license to the vSAN cluster.
vCenter 7.x
vCenter 8.x
vSAN 7
vSAN 8
Most of the time there is a scenario where customer is not able to apply the vSAN license as they are trying to assign the license from vCenter > Configure > Licensing.
You cannot assign the vSAN license from this point as this License is only for the vCenter.
The Correct method to assign the vSAN license using 2 methods
1. vSAN Cluster level.
Select the vSAN cluster and >then Configure tab> choose License from the left tab> On the right side you would see the Assign option.
Navigate to your vSAN cluster.
Click the Configure tab.
Under Licensing, select vSAN Cluster.
Click Assign License.
Select an existing license and click OK.
Configure License Settings for a vSAN Cluster (vmware.com)
If you have upgraded the vSphere/ vCenter then use the updated License keys accordingly.
Method1
Method 2