From Apple App Review Guidelines:

3.1.3(a) “Reader” Apps: Apps may allow a user to access previously purchased content or content subscriptions (specifically: magazines, newspapers, books, audio, music, and video). Reader apps may offer account creation for free tiers, and account management functionality for existing customers. Reader app developers may apply for the External Link Account Entitlement to provide an informational link in their app to a web site the developer owns or maintains responsibility for in order to create or manage an account. Learn more about the External Link Account Entitlement.

Netflix has a "Reader App" entitlement so if your app does not qualify as a Reader App, you likely cannot provide an external link for purchases under Apple's guidelines.