Attach the transaction hash of your USDT send

Not part of the documented sell flow: we take your USDT at create, from your balance or from your own wallet, so there is normally no hash to attach. If you do hold a hash for a sell order that is still awaiting_usdt, this records it against that order. That is all it does: it does not move the order, release a payout, or confirm that the USDT arrived. Deposit matching later looks for a deposit carrying this hash and exactly the order’s USDT amount, and only a match moves the order on; a deposit with this hash but a different amount is held for review, not paid. Your deposit address is the same for every order, so the hash is the only link we use — we never infer the order from the amount. Sell orders only: a buy order is refused with 409 ORDER_NOT_SELL_SIDE, and so is any order that has already left awaiting_usdt — including a sell order paid from your USDT balance at create — with 409 ORDER_NOT_AWAITING_USDT. The hash is 64 hexadecimal characters, with or without a 0x prefix, and is returned lower-case without the prefix. An order takes one hash, and a hash can fund only one of your orders: a different hash on an order that already has one is refused (409 TX_HASH_ALREADY_ATTACHED), never an overwrite — the first hash may already have been matched — and a hash already attached to another of your orders is 409 TX_HASH_ALREADY_USED. Re-sending the SAME hash is safe and returns 200, so a retry after a lost response is fine.