Hi Oscar,
The exercise you are referring to requires you to use your own subscription. It is not intended for you to use the sandbox, which is why there is no "Activate sandbox" button. Without an activated sandbox, you will not see "Concierge Subscription" show up in the portal.
Some exercises will allow/provide a sandbox for you, while others will not. Easy way to know if you can use a sandbox is if there is a Activate sandbox button, or, if a sandbox is already active, it will say Sandbox activated! Time remaining:. Please note that sandboxes expire after a certain amount of time. If you pause during a module for some reason and then come back, your sandbox may have disappeared/expired. To solve this you need to activate a new sandbox.
Please click Accept Answer if the above was helpful.
Thanks.
-TP