Why I can't download for free FreeFire?

Do you have a payment method tied to your account? The app is free. But the app offers in-app purchases and that requires you have a payment tied to your account.

Are you referring to this app in the Apple App Store: https://apps.apple.com/us/app/garena-free-fire-rampage/id1300146617?

If so, what happens when you try to download it? That is, are you seeing any error messages?

Your post doesn’t make much sense as written. Please read this→Writing an effective Apple Support Communities post, then post a description of your issue.