Nick here from Shopify. Good question!
I am wondering if you still have your store password protected in this instance? If you are still on the trial but have picked a plan, then you should be able to make a sale and accept orders as the checkout is open once you have picked a plan. You can check this in your store admin by taking the following steps or checking the link to the guide here.
From your Shopify admin, go to Online Store > Preferences.
Go to the Password protection area.
Uncheck Enable password.
It should look like the screenshot below where you would untick the box then to fully open your store.
Let me know!
All the best, Nick
No problem at all. Glad to hear it works! Even after you pick your plan during the trial, you still won't get charged for it until the trial ends so you can maximize it.