Microsoft account balance can be used for purchases, but if the balance is not enough to complete the purchase, another payment method registered to the Microsoft account is required to cover the remaining amount. Microsoft also states that account balance may not be used for certain in-app subscriptions or purchases.
For subscriptions specifically, prepaid subscriptions cannot have their payment method changed because they are prepaid. Subscription billing is managed from Services & subscriptions at https://account.microsoft.com/services/.
What to check:
- Confirm whether the PC Game Pass charge is higher than the available 1300 JPY balance. If it is, add another payment method so Microsoft can use the account balance first and charge the rest to the card or PayPal.
- Go to Services & subscriptions and check the subscription payment setup there rather than only in the Xbox app.
- If trying to use PayPal instead of a card, Microsoft requires the PayPal account to have a credit card or confirmed bank account as its funding source.
- If the subscription still only asks for a card, contact Microsoft Support for purchase or billing help.