Invoices are not sent automatically yet.
- PayPal or Stripe users may request an invoice to email@example.com
- Purchases made on iTunes store may be viewed in your account purchase history accessible directly.
The full process on iPhone/iPad is described below:
- Open your Settings > [your name] > iTunes & App Store.
- Tap your Apple ID, then tap View Apple ID. You might be asked to sign in with your Apple ID.
- Swipe up to Purchase History and tap it.
- Tap on the > to the right of the total billed charge to see details of an invoice, including the billing date and order ID.
- You can tap Resend at the bottom of the invoice details screen to get a new email receipt.
source : Apple’s support page