Why do bank card payments for in-app purchases sometimes delay?

Many merchants do what is known as <batch processing> where thousands or maybe 10s of thousands of charges are processed at the same time. This is fairly common with larger merchants like Walmart, Target etc.

The delay might be due to technical issues at the merchant, bank or Payment Network Operator (Mastercard, Visa, etc.) or even the network itself. It is also usually less expensive for the merchant to batch process.

If you purchased the products, yes, you must pay.

Apple Pay is not a payment method. It’s a payment system that keeps your personal and financial information secure. The funding for Apple Pay transactions is through a Payment Method in your Apple Wallet or Apple ID Account.

Is Apple the merchant? Is the bank notice from the payment method in your Apple ID Account?

Apple will normally combine purchases in a single batch and not immediately make the charge, there is nothing wrong with it.

click here ➜ How apps, content, and subscriptions from Apple are billed - Apple Support

And if you did make the purchases, of course you must pay for them. Charging you after the fact does not in any way exempt you from paying.

Did you think you were getting them for free?