Re: Unable to download free game from App Store on iPhone
You may need to check you are signed in (to your iPhone) with your correct Apple Account details:
Sign in to your Apple Account - Apple Support
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Seems Apple require we have a payment method listed in our Apple Account for the first time we use the App Store or iTunes, even if we only want to download free apps.
If you want: Check which payment methods Apple Can accept in your country or region:
Payment methods that you can use with your Apple Account - Apple Support
How to: Add a payment method to your Apple Account - Apple Support
You may need to allow 24 hours for Account changes you make to update and come into effect.
How to delete an Apple ID payment method if you have no active subscriptions:
Remove a payment method from your Apple Account - Apple Support