These are 12 to 16-character alphanumeric codes used to claim in-game rewards like diamonds or skins via the official Garena Rewards Redemption Site The Risks of Downloading Files named license key.txt

Downloading unknown files can infect your device with malware designed to steal personal data.

Many sites claiming to offer these keys require you to log in with your social media or game credentials, which can lead to your Free Fire account being stolen Invalid Data: