Each workspace on Railway requires its own separate Pro plan subscription. When you create a new workspace, you are prompted to subscribe to a plan for that workspace because billing is per-workspace. This is expected behavior - you can create multiple workspaces on Pro, but each one needs its own Pro subscription at railway.com/new/workspace.

Ok, got it. And I can have two hobby workspace's in same account? A services of each project are not accessible between each others if they are in a same workspace?

Yes, you can have multiple Hobby workspaces on the same account. When creating a new workspace, you choose whether it should be Hobby or Pro, and each workspace has its own separate subscription and billing. Regarding isolation, services in different projects within the same workspace cannot communicate with each other over the private network since private networking is scoped to a single project and environment. However, all projects within a workspace are visible to workspace members, so if you need access-level separation per customer, separate workspaces would be the way to go.