how do i buy more storage

There is something wrong with your account that cannot be fixed at your end

If you see a message that says "Your account has been disabled in the App Store and iTunes," contact Apple Support for help.

What is happening when you’re trying to buy storage?

Try and follow these instructions to buy more storage

1. Go to Settings, then tap your name. 
2. Tap iCloud, then tap Manage Account Storage or Manage Storage. Or scroll down and tap Upgrade to iCloud+.
3. Tap Buy More Storage or Change Storage Plan.
4. Choose a plan and follow the onscreen instructions.