Do you have a you are trying to install? Are you using a free or premium Tezfiles account?
Method 2: Integrating Tezfiles with JDownloader 2 via GitHub Extensions
What are you using (Windows, macOS, or Linux)?
Paste the downloaded GitHub plugin file into the hoster folder, replacing the old file if prompted. Restart JDownloader 2. Step 4: Add Your Tezfiles Account