Regarding the percentages, yes in countries that have tax included in the displayed prices Apple deducts that. The exact amounts that you will get (“proceeds”) in each case are shown in “schedule 2” to the developer agreement; you can also find them in a table in App Store Connect where you set the price for your app or IAP.
Note that only larger businesses should be paying 30% now, smaller businesses should be paying 15% to Apple.
Customers will get an invoice (or at least a receipt) from Apple for their purchases. You don’t see this invoice. Remember that the customer has bought the app from Apple, not from you. Your business’ transactions are with Apple, monthly.
If you need an invoice for your sale to Apple, you need to generate that yourself. Note you do not need to send the invoice to Apple; if your local laws require that you send invoices then I think that Apple have a postal address that you can send them to, but I guess they just destroy them. Note that currency conversions make generating this invoice interesting; personally I wait until Apple have made the payment so I know the exact amount in my local currency, and then I generate an invoice for that amount. This means my accounts software doesn’t have to deal with multiple currencies. If you want to show the customer-paid price and deductions on this invoice you could do that, based on the numbers in the financial reports, but it makes things more complicated than they need to be.
