Why i cant purchase 99$ inapp while my account balance is over 120?

See -> Change, add or remove Apple ID payment methods

Change, add or remove Apple ID payment methods – Apple Support (UK)

• set your Apple ID balance as your default payment.

If you're still unable to update your payment method, Contact Apple Support.

Click here for more support and assistance.

Hello,

This could be an issue with previous transactions on your account. In certain cases, Apple may disable your account in App Store and iTunes. You can contact Apple Support to resolve the issue.

Thanks for reaching out!

-Drake