I bought an iPhone at the Apple Store.where can I check the balance?

If you mean “Balance on your Apple Account” …

Settings -> Apple Account [Name] -> Payment & Shipping -> Payment Methods

Follow these steps:

1. Open App Store
2. Tap your profile (upper-right corner of the screen)
3. Under Account, tap your profile to open a pane that displays your account balance

If you are experiencing an issue not listed here, contact support.

Good luck! 👋🏼😉