How to get sales receipt for iPhone 11 Pro max

Check your Account > Purchases or contact the store where you bought it.

If you bought it from Apple directly, go to the Apple Store app on your phone, tap Search, then My Order Status and your purchases made within the last 24 months will be there.

Maybe slip of the finger. It may well be 18 months. But in the case of the OP, they need their receipt for iPhone 11, so if purchased directly from Apple will be accessible there.

They are now showing 24 months? Used to be 18.....