Cannot add user to a workspace

Hello, In Oracle Primavera Cloud I'm trying to add a user to a workspace but it won't let me.

I go to Global Admin -> Users -> "User x" -> Manage Access . But the Assign option in Workspaces tab is not enabled.

I also go to Workspaces -> "Testing " workspace -> Summary & Settings - Security - Assign, but the user is not shown in list.

Also try to give acces in the same menu but in User Groups, but the user is not shown

Other information:

• The user is ACTIVE and has Schedule license assigned.
• All my user groups have access to that workspace.