Paid subscription begins immediately after the free trial is over
When you visit the settings page, you will see a notification that to keep the limits working the 14-day trial agreement needs to be accepted.
Once you decide to publish the limits for the first time, you will be redirected to a subscription page provided by Shopify where you are suggested to activate a new subscription plan with a 14-day long trial period embedded into it.
Once the subscription is activated, you will see the main settings page as displayed on the screenshot below.
This behavior is the regular Shopify app billing protocol. When the subscription was being activated for the first time you were supposed to be specifically asked by Shopify if you're sure you want to start paying for our services once the trial period is over.
If you believe this wasn't done, or that the activation page was misinforming, could you please contact https://support.shopify.com/ and ask them to take a look into this situation.
For more details, we provide customer support via email. Please send your questions or feedback to firstname.lastname@example.org. We look forward to providing you with assistance.