Idempotency keys

When a send times out or the connection drops, you can’t tell whether the transaction reached the chain. Retrying might send it twice, and not retrying might lose it. Starting in 10.1.0, you can attach an idempotency key to a send. Portal broadcasts a key at most once while it remembers the key (at least 24 hours), so a retry with the same key within that time cannot send the same transaction twice. Idempotency keys are optional. Requests without one behave exactly as before.

Supported requests

Entry point	Where to pass the key	Supported on
`portal.request(chainId, method, params, options)`	`RequestOptions(idempotencyKey = ...)`	`eth_sendTransaction`, `sol_signAndSendTransaction`, `sol_signAndConfirmTransaction`
`portal.sendAsset(chainId, params)`	`SendAssetParams(idempotencyKey = ...)`	EVM (`eip155`) and Solana chains

Portal enforces the key whether the transaction is signed on the device or through the Enclave MPC API (useEnclaveMpcApi).

Generate a key

// io.portalhq.android.utils
fun generateIdempotencyKey(): String

generateIdempotencyKey() returns a lowercase UUID v4. Generate one key per operation, such as one transfer or one payment, and store it with the pending operation before you send. A retry, even one after the app restarts, can then reuse it. You can also use your own key, for example an ID from your backend. The SDK trims surrounding whitespace, and the key must then follow these rules:

Rule	Detail
Length	1–255 characters
Allowed characters	`A-Z`, `a-z`, `0-9`, `-`, `.`, `_`, `~`

A key that breaks these rules throws PortalException.Provider.InvalidIdempotencyKey before the user is asked to approve the request, so nothing is signed or sent.

Send a transaction with a key

Build the transaction once, then send it with the key:

import io.portalhq.android.api.data.buildtransaction.BuildTransactionParam
import io.portalhq.android.provider.data.PortalRequestMethod
import io.portalhq.android.provider.data.RequestOptions
import io.portalhq.android.utils.generateIdempotencyKey

val chainId = "eip155:11155111" // Ethereum Sepolia

// Build the transaction once. A retry sends this same transaction.
val txDetails = portal.api.buildEip155Transaction(
    chainId = chainId,
    params = BuildTransactionParam(
        to = "0xDestinationAddress",
        token = "USDC",
        amount = "1",
    ),
).getOrThrow()

// One key per transfer. Store it with the pending transfer.
val idempotencyKey = generateIdempotencyKey()

val result = portal.request(
    chainId = chainId,
    method = PortalRequestMethod.eth_sendTransaction,
    params = listOf(txDetails.transaction),
    options = RequestOptions(
        signatureApprovalMemo = "Send USDC",
        idempotencyKey = idempotencyKey,
    ),
)

println("✅ Transaction hash: ${result.result}")

On Solana, build the transaction with portal.api.buildSolanaTransaction(chainId, params) and send it with PortalRequestMethod.sol_signAndSendTransaction or PortalRequestMethod.sol_signAndConfirmTransaction the same way.

Retry with the same key

If a send fails and you don’t know whether the transaction went out, for example after a timeout, call portal.request(...) again with the same transaction and the same key. One of two things happens:

The first attempt never reached Portal, so Portal has no record of the key, and the retry sends the transaction.
Portal already recorded the key, whether that attempt is still in progress, was broadcast or failed, and it rejects the retry with PortalException.Mpc.MpcResultError instead of broadcasting again.

Reuse a key only for the identical request. If anything changes, such as the amount, the recipient, the chain or the method, generate a new key.

Handle a rejection

Two extension functions on PortalError (in io.portalhq.android.utils.errors) identify an idempotency rejection. Call them on the exception’s error:

Function	`true` when
`isIdempotencyRejection()`	`id` is any of the idempotency error IDs below.
`isIdempotencyKeyReused()`	`id` is `IDEMPOTENCY_KEY_REUSED`.

Branch on id to decide what to do next. Each ID is also available as a constant on PortalIdempotencyErrorId (in io.portalhq.android.utils):

Error ID	What it means	What to do
`IDEMPOTENT_REQUEST_IN_PROGRESS`	A request with this key is still being processed.	Wait, then retry with the same key.
`IDEMPOTENT_REQUEST_ALREADY_COMPLETED`	The transaction was broadcast.	Don’t send it again. Look the transaction up on-chain.
`IDEMPOTENT_REQUEST_PREVIOUSLY_FAILED`	The earlier request failed, or its outcome is unknown. Portal returns this ID in both cases, so it doesn’t confirm that the transaction was not broadcast.	Check the chain before sending again with a new key.
`IDEMPOTENT_REQUEST_UNEXPECTED_STATE`	Portal can’t confirm the outcome of the earlier request.	Check the chain before sending again with a new key.
`IDEMPOTENT_TX_MISSING`	Portal can’t find the request recorded for this key.	Check the chain before sending again with a new key.
`IDEMPOTENCY_KEY_REUSED`	The key was already used for a request with a different payload. This doesn’t tell you the state of that earlier request.	Check the chain before sending again with a new key.

import io.portalhq.android.exceptions.PortalException
import io.portalhq.android.provider.data.PortalRequestMethod
import io.portalhq.android.provider.data.RequestOptions
import io.portalhq.android.utils.PortalIdempotencyErrorId
import io.portalhq.android.utils.errors.isIdempotencyRejection
import java.io.IOException

try {
    val result = portal.request(
        chainId = chainId,
        method = PortalRequestMethod.eth_sendTransaction,
        params = listOf(txDetails.transaction),
        options = RequestOptions(idempotencyKey = idempotencyKey), // The key stored with this transfer
    )

    println("✅ Transaction hash: ${result.result}")
} catch (e: PortalException.Mpc.MpcResultError) {
    when {
        !e.error.isIdempotencyRejection() ->
            println("❌ Signing failed: ${e.message}")
        e.id == PortalIdempotencyErrorId.IDEMPOTENT_REQUEST_IN_PROGRESS ->
            println("⏳ Still processing. Retry later with the same key.")
        e.id == PortalIdempotencyErrorId.IDEMPOTENT_REQUEST_ALREADY_COMPLETED ->
            println("✅ Already broadcast. Look the transaction up instead of sending it again.")
        else ->
            println("⚠️ Outcome unconfirmed (${e.id}). Check the chain before sending again with a new key.")
    }
} catch (e: IOException) {
    // No answer about the broadcast, for example a timeout. Retrying with the same key is safe.
    println("❌ Send failed: ${e.message}")
}

No rejection returns the original transaction hash. Before you send an operation again under a new key, check the chain or your transaction history to confirm the first attempt didn’t land. Portal treats a new key as a new transaction.

Match rejections on id, not on the error message or code.

Retry `sendAsset`

Pass the key in SendAssetParams. sendAsset returns a Result, so a rejection arrives as its failure:

import io.portalhq.android.data.SendAssetParams
import io.portalhq.android.exceptions.PortalException
import io.portalhq.android.utils.errors.isIdempotencyRejection
import io.portalhq.android.utils.generateIdempotencyKey

// One key per transfer. Store it with the pending transfer.
val idempotencyKey = generateIdempotencyKey()

portal.sendAsset(
    chainId = "eip155:11155111",
    params = SendAssetParams(
        to = "0xDestinationAddress",
        amount = "0.0001",
        token = "NATIVE",
        signatureApprovalMemo = "Send ETH",
        idempotencyKey = idempotencyKey,
    ),
).onSuccess { response ->
    println("✅ Transaction hash: ${response.data?.txHash}")
}.onFailure { e ->
    if (e is PortalException.Mpc.MpcResultError && e.error.isIdempotencyRejection()) {
        println("Portal already handled this key: ${e.id}")
    } else {
        println("❌ Send failed: ${e.message}")
    }
}

sendAsset builds the transaction again on every call, and Portal compares a retry with the request it first received under the key before it checks that request’s status:

EVM: the rebuilt transaction normally matches the first one, because Portal fills in the nonce and gas when it signs. A retry gets the status of the first request, as described in Handle a rejection.
Solana: each build carries a new recent blockhash, so a retry with the same key is normally rejected with IDEMPOTENCY_KEY_REUSED, whatever happened to the first attempt.

Either way, while Portal remembers the key, the transfer is never broadcast twice under it. Before you retry with a new key, wait until the first transfer can no longer land, then check the chain:

Solana: wait until the first transfer is confirmed or its recent blockhash has expired, about 60–90 seconds after the transaction was built.
EVM: wait until the first transfer is confirmed or the account nonce has moved past it.

For the most predictable retries, especially on Solana, build the transaction once and send it with portal.request(...) as shown in Send a transaction with a key. Every retry then gets the status of the first request, including IDEMPOTENT_REQUEST_IN_PROGRESS.

Requests that don’t take a key

Request	With a key
`eth_sendRawTransaction`, `sol_sendTransaction`	Throws `PortalException.Provider.IdempotencyKeyUnsupported` before anything is sent. These methods broadcast a transaction that is already signed through a plain RPC call, which Portal can’t deduplicate.
`sendAsset` on a Bitcoin chain	Fails with `PortalException.Provider.IdempotencyKeyUnsupported` before the transaction is built.
Any other method, such as `eth_signTransaction` or `personal_sign`	The SDK ignores the key and logs a warning when the log level is `PortalLogLevel.WARN` or more verbose.

How long Portal remembers a key

Portal remembers a key for at least 24 hours after the request was last updated, then removes it. Once the key is removed, the same key is treated as a new request. Because the exact removal time isn’t fixed, check the chain before you retry an operation that is older than 24 hours, whatever key you use.

Presignatures

If you enable presignatures (usePresignatures in FeatureFlags) and a presignature attempt fails after reaching Portal, the SDK’s fallback sign reuses the key. Portal can reject it, for example with IDEMPOTENT_REQUEST_IN_PROGRESS or IDEMPOTENT_REQUEST_PREVIOUSLY_FAILED, where a request without a key would have been signed. Handle it like any other rejection.

Next Steps

Learn about signing transactions
Read Send tokens for the full sendAsset flow
Review Error handling for the PortalException hierarchy
See Idempotency keys for the Enclave MPC API

Getting Started

SDKs

APIs

Integrations

Resources

Idempotency keys

Supported requests

Generate a key

Send a transaction with a key

Retry with the same key

Handle a rejection

Retry `sendAsset`

Requests that don’t take a key

How long Portal remembers a key

Presignatures

Next Steps

​Supported requests

​Generate a key

​Send a transaction with a key

​Retry with the same key

​Handle a rejection

​Retry sendAsset

​Requests that don’t take a key

​How long Portal remembers a key

​Presignatures

​Next Steps

Supported requests

Generate a key

Send a transaction with a key

Retry with the same key

Handle a rejection

Retry `sendAsset`

Requests that don’t take a key

How long Portal remembers a key

Presignatures

Next Steps