For active customers with an ApprovalMax subscription, the trial period for new Organisations is limited to 3 days. So, you can add another client Organisation without buying a subscription right away.
When you add a new Organisation for your client, you have 3 days to work on the workflows and make sure that everything is set up correctly and working as expected.
If the client chooses after the free trial to continue using ApprovalMax, you'll need to add this Organisation to your billing.