In our Backfill server API documentation, we currently state:
Ticket ID — Provide a
matchmaking ticket ID (or opt to have them autogenerated). You can
use the same mechanism to assign ticket IDs to both matchmaking and
backfill requests. Tickets for matchmaking and backfilling are
processed the same
Unfortunately, you must provide a ticket ID – one will NOT be autogenerated, currently.
We have added a tracking issue to our backlog and will update this post when the fix for this issue has been released. Sorry for the inconvenience.