SP Online rest api: how to get the "author byline field"?

This gets the name in the "created by" field fine, but for news posts I need the "author byline" field:

https://xxx.sharepoint.com/sites/xxx/_api/web/lists/getbytitle('Site Pages')/items?$select=Title,FileRef,CanvasContent1,Videourl,BannerImageUrl,Author/Title&$expand=Author&$filter=ID eq '193'

The internal field name is "_AuthorByline" but the response is that doesn’t exist. Does the field have to be a managed property for the api call to work?

I should add that in a search rest api, "Author" returns the "AuthorByline" field, if populated, "created by" if not..

/_api/web/lists/getbytitle('Site Pages')/items?$select=OData__AuthorByline/Title&$expand=OData__AuthorByline&$filter=ID eq '<pageid>'