I’m trying to do subscriptions on my Apple account and there’s a balance on my payment method but it keep declined anytime I’m trying to access it

i have an available balance on my account

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.

👉 How to change your payment method on your iPhone, iPad or iPod touch

1. Open the Settings app.
2. Tap your name.
3. Tap Payment & Shipping. You may be asked to sign in with your Apple ID.
4. From here, you can do these things:

• • 
  • Add a payment method – tap Add Payment Method.
  • Update a payment method – tap the payment method, then edit your information. You may need to enter the security code that's printed on your credit or debit card. If you use the card with Apple Pay, go to the Wallet app to edit the card information.
  • Remove a payment method – tap Edit, tap the red Delete button, then tap Remove. If you have an unpaid balance, have subscriptions, including an iCloud storage plan, or use purchase sharing, you can't remove all payment methods. Find out how to remove all payment methods.
  • Change the order of your payment methods – tap Edit, then drag the move order icon .*

Click here for more support and assistance.

You have already done it, you see your Apple ID balance -> Credit: $15.00

Click here for more support and assistance.