# Unable to release or send coins from contract — missing mt\_index / QualifiedCoinInfo after receive() - jeyem7843 **URL:** \ **Category:** Technical Questions\ **Created:** [October 27, 2025, 10:00am UTC](https://forum.midnight.network/t/unable-to-release-or-send-coins-from-contract-missing-mt-index-qualifiedcoininfo-after-receive-jeyem7843/563 "2025-10-27T10:00:18Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Discord\_Dev\_Query](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@Discord\_Dev\_Query](https://forum.midnight.network/u/Discord_Dev_Query)\ **Post date:** [October 27, 2025, 10:00am UTC](https://forum.midnight.network/t/unable-to-release-or-send-coins-from-contract-missing-mt-index-qualifiedcoininfo-after-receive-jeyem7843/563/1 "2025-10-27T10:00:18Z")
`What are you trying to do?` I’m building an escrow-style contract that should be able to both receive and later release coins. ```fn fn send(input: QualifiedCoinInfo, recipient: Either, value: Uint<128>) { ... } ``` Receiving works fine — the contract correctly accepts assets via receive(coin). However, when I attempt to release the assets (send them back out), I need to pass a valid QualifiedCoinInfo, which includes the coin’s mt\_index (Merkle tree index). Without the correct mt\_index, the contract cannot identify and spend the coin it holds. `What’s not working or unclear?` The documentation explains that: The runtime or indexer already knows the mt\_index of each coin’s commitment when the contract receives it. DApps are supposed to register this mapping by calling: ```auto queryContext.insertCommitment(commitment, index); ``` The problem is: There is no documented or programmatic way for a DApp to obtain that mt\_index (or the commitment) from the indexer or runtime after the contract has received the coin. As a result: I can receive coins, but cannot later construct the required QualifiedCoinInfo. Therefore, the contract cannot release or send out the assets it holds. This effectively prevents implementing escrow or similar holding/spending patterns. Questions: How can a DApp obtain the correct mt\_index for a coin commitment after it’s received by a contract? Is there an API (current or planned) in the indexer or runtime to expose this data? How should insertCommitment() be used in practice if we can’t access the index value? `What have you tried so far?` Used the indexer’s Zswap state to estimate the Merkle index: ```auto const mt_index = zswapState.firstFree - 1; ``` This works inconsistently — only when no other commitments are inserted in the same block. Reviewed all available docs (docs.midnight.network/develop) — including Contracts, QueryContext, and Coin Handling Proposal — none describe how to fetch mt\_index or register it off-chain. Contacted support earlier — they confirmed the runtime knows the index, and suggested using queryContext.insertCommitment(commitment, index) — but provided no example or way to retrieve those values. Verified that the issue is not within contract logic — it’s strictly about obtaining mt\_index to build a valid QualifiedCoinInfo. Example of the blocked step: ```auto // Construct QualifiedCoinInfo for release const input = { coin: { nonce: deposit.nonce, type: deposit.type, value: deposit.value }, mt_index: ??? // this is required but unknown }; // Attempt to send/release contract.send(input, depositorPublicKey, deposit.value); ``` Without access to the mt\_index, the transaction can’t be signed or validated, so the contract cannot release assets it holds. `Add any relevant code or error messages.` ```auto ``` ---
**Author:** ![sergeykisel](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@sergeykisel](https://forum.midnight.network/u/sergeykisel)\ **Post date:** [October 27, 2025, 2:07pm UTC](https://forum.midnight.network/t/unable-to-release-or-send-coins-from-contract-missing-mt-index-qualifiedcoininfo-after-receive-jeyem7843/563/2 "2025-10-27T14:07:42Z")
> [@Discord\_Dev\_Query](#): > > However, when I attempt to release the assets (send them back out), I need to pass a valid QualifiedCoinInfo, which includes the coin’s mt\_index (Merkle tree index). There are two possibilities to send, either you use `sendImmediate` which accepts `CoinInfo` as input and immediately sends coins available in the same circuit from the wallet of the user who calls that circuit. Normal call `send` accepts `QualifiedCoinInfo` which is the one written on the ledger, so when you receive a coin to your contract - you should be writing it to the ledger with `writeCoin` which writes ``QualifiedCoinInfo`` to the ledger which you can send later from another transaction. ---
**Author:** ![bochaco](https://yyz2.discourse-cdn.com/flex010/user_avatar/forum.midnight.network/bochaco/32/112_2.png) [@bochaco](https://forum.midnight.network/u/bochaco)\ **Post date:** [October 27, 2025, 3:35pm UTC](https://forum.midnight.network/t/unable-to-release-or-send-coins-from-contract-missing-mt-index-qualifiedcoininfo-after-receive-jeyem7843/563/3 "2025-10-27T15:35:29Z")
> [@I’m developing an escrow-style contract that needs to both receive and later release coins using the documented methods](https://forum.midnight.network/t/i-m-developing-an-escrow-style-contract-that-needs-to-both-receive-and-later-release-coins-using-the-documented-methods/562/2): > > If I understand your doubt correctly, I believe you are referring to something like the following for deposits: // Contract's own treasury of native tokens. export ledger treasury: QualifiedCoinInfo; export circuit depositFunds(coinInfo: CoinInfo): [] { assert(coinInfo.color == nativeToken(), "Only native tokens can be deposited"); receive(disclose(coinInfo)); const me = right\(kernel.self()); treasury.writeCoin(disclose(coinInfo), me); return []; …