To get started, the card provided is a US card and would only work in a US Apple store.
Here's a guide on how to switch your store to a US store on your phone. You can open the Settings app.
Tap your name, then tap Media & Purchases.
Tap View Account. You might be asked to sign in.
Tap Change Country or Region.
Tap your new country or region, then review the Terms & Conditions.
Tap Agree in the upper-right corner, then tap Agree again to confirm.
Select a payment method, enter your new payment information and billing address, and tap Next.
Yaay!! You can now make payments on Apple using your Grey Virtual USD card; Please ensure your card is fully funded before making any payment.
Declined Apple Payment
Once you have successfully added your card by following the steps above and payment failed, this is likely due to insufficient funds; please ensure you have enough funds to pay for all your subscriptions.