At the account creation, a "Trial" voucher of 30€ is added to your account with "Professional" plan. This voucher is valid for 3 month or until you finish your credits.
This credit is equivalent to a usage of 3 servers for 1 full month with "Pofessional" plan.
If your voucher is completely used or its end date is passed, your account will automatically switch to the "Free" plan. You can after adding a payment mean switch back to any plan at any time.