How is a fixture that was created by mistake handled? Is it always communicated via CANCELLED, or is there another parameter or workflow for this case?

Mistakenly created fixtures are always communicated as CANCELLED; there is no other parameter or workflow in such cases. Further detailed information can be obtained via the client’s 24/7 Oddin.gg Trading chat, while the market void_reason_id within the Bet Cancel messages carries the reason.