Follow these configuration to allow author add Rooms into their listing

Edit listing type post to select Hotel Room for child post type option then click Save Changes

Add/edit room submit fields

You also need add Calendar field to change room’s available dates

Add Listing Rooms field on listing submit/edit page

Then author can add/edit rooms for their listing

Please make sure that room must have quantity and person fields

And to show rooms on single listing page. Edit listing type post -> Single tab -> Listing sub-tab to add Hotel Rooms element into layout builder.

And this is how rooms showing on listing page

Edit room details page

Set Hotel Room Dates for Dates from option of Availability Calendar element on listing page to show available dates for booking ( dates from the room calendars )