it will simply decline your payment because you don’t have enough.
If your payment method is declined in the App Store or iTunes Store, see ->
If your payment method is declined in the App Store or iTunes Store - Apple Support
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How to complete your purchase if a payment failed or was declined
- On your iPhone or iPad, open the Settings app.
- Tap your name.
- Tap Payment & Shipping.
- Add a different payment method and remove the old one.
- Try to complete your purchase.
If you still can't make a purchase
Check also here -> If you can’t download or update apps on your iPhone or iPad
If you can’t download or update apps on your iPhone or iPad – Apple Support (UK)
scroll to point 2 & 3 ⤵️
Add a payment method
You may need to have a valid payment method on file, even if the app you want to download is free.
Add a payment method
Resolve a problem with your payment method
If your payment method has expired, declined or failed, or a message says "There is a Billing Problem with a Previous Purchase"
See also the following Apple articles:
Payment methods you can use with your Apple ID
Payment methods you can use with your Apple ID – Apple Support (UK)
fyi: Not all credit & debit cards seem to work with App Store / iTunes Store, try a different one, or preferably a credit card. If your card is not accepted as a paymenf method, you need to contact your bank.
Add a payment method to your Apple ID
Add a payment method to your Apple ID – Apple Support (UK)
- If you want to change your card, you need to add first the new card, then remove the old card.
- or if you want to use your Apple Account balance, you need to set your Apple Account balance as your default payment.
Add money to your Apple Account balance -> Add money to your Apple Account balance - Apple Support
Check your Apple Account balance -> Check your Apple Account balance – Apple Support (UK)
If you update your payment method or add funds to your Apple Account balance, It would take about 1 to 3 business days in order to process.
If you're still unable to update your payment method, Contact Apple Support.
If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK)