Thanks for backing an indie app. Two steps to unlock Pro:
Polar just emailed it to you (subject: “Your license key”). It's also in your Polar purchases.
Menu bar → 设置 / Settings → 账户 / Account → paste the key. Pro unlocks instantly on every Mac you use it on.
中文用户：菜单栏 → 设置 → 账户 → 粘贴 License Key 即解锁。