Cancel a match

Cancels a match as the personal API key owner. For a regular match the owner must be able to manage it (be a captain, co-captain, or org owner of a participating team, or an admin); past the league grace period an accepted league match is treated as a forfeit. For a PENDING challenge the owner must lead the creator team (captain, co-captain, or org owner of the challenging team), and past the challenge grace window (default 24h, league-overridable) cancelling any pending challenge - league or not - is recorded as a forfeit with the creator team taking the loss. Requires matches.user_matches:read-write and API writes access. Supports an optional Idempotency-Key header for safe retries.