How to authorize to Approve/Create backfill ticket REST API?

Hello, I have a question, I got auth token using token-exchange Rest API, so I have ability to create simple tickets, but I can’t find right way to authorize to make actions with backfill tickets. As I understand, when I will have backfill ticket id, I should approve it, so I wanna use Rest Api for this action. Also, I could have a wrong view and it can’t be done by Rest, could you confirm it?
Thank you for feedback!

Backfill API: Unity Services Web API docs

If you expand the Authorization section, there’s an explanation of how to authorize for backfill requests.

Okay, how could I find GameServerHosting ip? Could you please help to understand, do I need to configure something, or just use already hosted service?

A few things here,
If backfill is enabled on the matchmaker configuration, if a server starts and is not full, matchmaker creates a backfill ticket automatically. No need to create one yourself.
The server when it starts can get the information of the backfill through the matchmaking result (see here: Integrations with other UGS services)
In those matchmaking result, there is a backfill ticket id, you should just approve this one and ticket will be directly assigned to the server associated to that backfill ticket.

When approving a backfill ticket, the API returns the updated backfill ticket with all the players added to the match.

On another hand, the server.json file on the Multiplay server contains the IP:port for the server. See here Server.json

I hope that helps !