I logged into Cloud Playground to follow along with this demo.
There’s even a pop up message "If you have access to our Cloud Playground you can choose to follow along to this demo lesson in your own sandbox environment. If you choose to use your own Cloud account for this demo, please be aware you could incur charges."
I can’t seem to do anything with the Cloud Playground demo account relating to billing.
I can go to the Linked Billing Account and view some data, but I can’t Manage Billing Accounts, or Add Billing Account, as I don’t have the "Billing Account Creator" permission in the sandbox.
Just FYI in case you are actually trying to follow along with the demo using Cloud Playground.