Link to section:
https://docs.parseplatform.org/parse-server/guide/#configuring-parse-server-for-sign-in-with-apple

What is the issue?
It is mentioning that you can use client_id. That might have been true in the past, but now the correct way is to use clientId.

Can you propose a solution?
Correction to:

{
  auth: {
   apple: {
     clientId: "my_apple_service_identifier", // optional; provides extra validation; replace with your Service ID provided by Apple
   }
  }
}

First reported by @ChrisEelmaa in parse-community/parse-server#6858.