Are you sure Netflix is able to do this (genuine question)? According to this[0] article, Apple says that apps that target consumers (as opposed to businesses) must allow the user to sign up for the service from within the app:
> Apple allows these kinds of client apps — where you can't sign up, only sign in — for business services but not consumer products. That's why Basecamp, which companies typically pay for, is allowed on the App Store when Hey, which users pay for, isn't. Anyone who purchased Hey from elsewhere could access it on iOS as usual, the company said, but the app must have a way for users to sign up and pay through Apple's infrastructure.
> Apple allows these kinds of client apps — where you can't sign up, only sign in — for business services but not consumer products. That's why Basecamp, which companies typically pay for, is allowed on the App Store when Hey, which users pay for, isn't. Anyone who purchased Hey from elsewhere could access it on iOS as usual, the company said, but the app must have a way for users to sign up and pay through Apple's infrastructure.
[0] https://www.protocol.com/hey-email-app-store-rejection