If you purchased a subscription through Google Play, it should activate automatically as long as you are signed into the same Google account.

Increases your MobiDrive capacity from 5GB to 50GB. How to Install and Activate File Commander Premium

The process for activating a premium key typically involves linking it to your MobiSystems account. Step 1: Install the App

If you have a standalone activation key (often provided with device bundles or promotional purchases):

Allows you to restore accidentally deleted files from internal storage or SD cards.

Unauthorized apps do not receive security updates, leaving your personal "Vault" files vulnerable. Troubleshooting