Free iPhone cleaner

You can download free apps, but you may need to have a valid payment method on file, even if the app you want to download is free. 

You can have a credit card / debit card on file and an Apple Account balance.

If you have set your Apple Account balance as your default payment method, your default payment method will be used first by Apple when you need to make a payment.

Free apps has also In-app pruchase.

If you are talking abut this app, it is Free with Offers In-App Purchases.

• Disclaimer: This app is free to download, but you will be required to sign-up for an auto-renewing subscription to access the app's full functionality.

I'll add that any "cleaning" app you see for any Apple product is essentially worthless or can even possibly mess things up on your device. I don't know if you know the term "snake oil"...