You're likily seeing this error due to not having selected a plan and adding a payment method to your store. When a store is in trial the checkout is disabled and will not allow customers to place orders in your store unless a plan is selected. If you navigate to Settings/Plans and Permissons you will be able to select a plan, add a payment method, and enable your checkout. You will also be able to remove the store password in Online Store/Preferences. It is important to note that selecting a plan while in a trial will not charge you until your trial time runs out; however, it will enable your checkout process and allow you to launch your store.
Let me know if you have any questions!