[Channel App] Push Endpoint: How to use author#fields ?

Hi there,

I am struggling to understand the push endpoint documentation on how to set the fields for the author ?

Let's say this is the author object:

{
"external_id": 1,
"fields": [] 
}

How do I add the email to the fields array ?

The description of the attribute says:
> Array of items containing user field identifier ('id') and value of field ('value'.) For system fields ('notes' or 'details'), the identifier is the English name. For custom fields, the identifier may be the ID or the name

But when adding it as “fields”: [{"email": “something@example.com”}], the email does not show up.

Am I restricted to only notes and details ? If so, do I add them as key value pairs
[{"notes": “a note”}, {"details": “some details”}] ?

Thank you for your help.