Assigning Security Group to Workspace via Admin Portal

Hi,

Got a weird issue...I'm trying to use the Admin portal, Workspaces section to give a Security Group access to a workspace.

However the security group isn't recognised when I start to type it in so I can't assign access:

However if I go to the Access settings in the workspace itself and start to type in the group name it is recognised and I can apply it:

I am using the same account (Power BI Administrator Role) to attempt both of these.

Any ideas?

Thanks

Mark