You can purchase Threema directly from the Apple App Store or Google Play Store.
For Android users who want to avoid Google, Threema sells licenses directly on their website. These are official "License Keys." Threema License Key Extra Quality Free
Threema is a paid, privacy-focused messaging app, and official "free" license keys do not exist outside of specific promotions or enterprise trials You can purchase Threema directly from the Apple
Follow these simple steps to get your free Threema License Key: privacy-focused messaging app