Unfortunately, once you have subscribed to a plan, you cannot revert to the free trial. We do this to enforce a one-way transition from a free trial to a paid subscription, which prevents users from exploiting the free trial period multiple times.
Once a subscription is active, the system registers the account as a paying customer, and the option to return to the free trial is disabled.
If you have any questions during your free trial - please don't hesitate to reach out!