No, our apps never ask for money while you still have a valid license or subscription. We have not added an option to buy while there is an active subscription to prevent accidental double purchases.
On iOS and based on how the App Store works, the trial time is simply a free month at the beginning of a regular subscription. To switch, e.g., to the one-time purchase, please cancel your subscription and let it expire. As soon as the app asks for a license again, choose your desired option.