Pending purchase

Sometimes, a pending purchase could mean that the payment has not been approved or released by the bank or financial institution through your payment method. And if you can check the payment information settinga in your iPhone, you may see a message that the payment method has been declined

If your payment method has been declined in the App Store or iTunes Store – Apple Support (AU)

To answer your question, yes, you cna definitely use your Apple ID balance for that. You may also want to check this article for other payment methods that you can use:

Payment methods that you can use with your Apple ID - Apple Support

Hope that helps. Best of luck!

Pending purchase -> The merchant is still finalizing the purchase. Once that’s complete the amount may update, so it has not been charged to your bank account yet. 

It would take about 1 to 2 business days in order to process.

Then yes, if you use your Apple ID balance as payment method.