The trial is 7 days, tracked server-side by your hardware fingerprint. It starts at your first successful transcription and decrements one day every 24 hours. Because it's tied to the physical machine, uninstalling and reinstalling the app — or even reinstalling macOS — does not reset it. Only a different physical machine gets a fresh 7 days.
On expiry, transcription returns an error and the app shows "Trial ended". The menu then shows "Unlock Full Version", which opens a Stripe checkout carrying this machine's fingerprint. After you pay, the app unlocks automatically on this machine.
Your purchase email contains a recovery key that starts with "VF-". To activate Voicefall on a machine, use the menu item "Enter Recovery Key…" and paste the key. One key activates up to 3 devices (up to 3 Macs), so you can use your license across your own machines.