# Raw Custom Instruction

> Performing custom function calls in the Flare Smart Accounts by carrying the full PackedUserOperation in the XRPL memo.

> For the complete documentation index, see [llms.txt](/llms.txt). Markdown versions of documentation pages are available by appending `.md` to the page URL.

Source: https://dev.flare.network/smart-accounts/raw-custom-instruction

The **raw custom instruction** (memo opcode `0xFF`) is a single-actor variant of the [Custom Instruction](/smart-accounts/custom-instruction): instead of committing to a `keccak256(userOp)` hash and relying on an executor to deliver the bytes, the XRPL `Payment` memo carries the entire ABI-encoded `PackedUserOperation` inline immediately after a 10-byte header. The user signs the XRPL `Payment`, ships the payload on XRPL, and the smart account replays the user operation on Flare with no further off-chain data.

The recommended path is the [Custom Instruction](/smart-accounts/custom-instruction) - it lifts the XRPL memo size cap and is what the rest of the smart-accounts tooling defaults to. Reach for the raw variant when you do not want to operate or coordinate with an executor and your call batch fits inside the XRPL memo cap. The [comparison guide](/smart-accounts/custom-instruction-comparison) breaks down when each is appropriate.

This page covers only what differs from the [Custom Instruction](/smart-accounts/custom-instruction). For the [`PackedUserOperation` construction](/smart-accounts/custom-instruction#user-operation-payload) (`sender`, `nonce`, `callData`), the [`Call` struct](/smart-accounts/custom-instruction#executeuserop-and-the-call-struct), and how to [build `callData` in TypeScript](/smart-accounts/custom-instruction#building-calldata-in-typescript), refer to the [Custom Instruction page](/smart-accounts/custom-instruction).

No destination tags

XRPL transactions targeting smart accounts must not use a destination tag. A destination tag forces [FAssets direct minting](/fassets/direct-minting) to credit the tag-holder, which would let an unrelated party front-run the user operation.

## Memo Layout[​](#memo-layout "Direct link to Memo Layout")

The XRPL memo carries a 10-byte instruction header followed by the ABI-encoded `PackedUserOperation`:

Bytes

Field

Meaning

`0`

`instructionId`

`0xFF` - raw custom instruction

`1`

`walletId`

One-byte wallet identifier assigned by Flare; `0` if not registered

`2-9`

`executorFeeUBA`

Executor fee in the FAsset's smallest unit, big-endian `uint64`

`10+`

`userOpData`

`abi.encode(PackedUserOperation)` - the call payload the controller decodes

The total memo length is `10 + len(abi.encode(userOp))` bytes. The XRPL caps each memo at `1024` bytes, so large or repetitive call batches must be split across multiple XRPL payments - each of which pays its own FAssets minting fee and executor fee - and a single call whose ABI-encoded calldata alone exceeds the budget cannot be expressed at all without deploying a shim contract on Flare to compress it.

## Dispatch Flow[​](#dispatch-flow "Direct link to Dispatch Flow")

A single XRPL payment drives the whole flow: the FAssets `AssetManager` mints FXRP into the smart account, calls `MasterAccountController.handleMintedFAssets`, and the controller decodes the `PackedUserOperation` directly from the memo bytes (no `_data` parameter, no hash check) before dispatching `executeUserOp` on the personal account. There is no executor split: any indexer that observes the XRPL payment can submit the FDC proof through `executeDirectMinting(proof)`, and the `MasterAccountController` validates the same `sender`, `nonce`, and `callData` fields as for the [custom instruction](/smart-accounts/custom-instruction#user-operation-payload).

## Replay Protection[​](#replay-protection "Direct link to Replay Protection")

Each personal account maintains a monotonically increasing nonce, accessible via [`getNonce`](/smart-accounts/reference/IMasterAccountController#getnonce). A successful `executeUserOp` increments the nonce and emits [`UserOperationExecuted`](/smart-accounts/reference/IMasterAccountController#useroperationexecuted), so the same `PackedUserOperation` cannot be re-executed. The XRPL transaction ID is also recorded in the controller to prevent the same payment from being submitted twice.

## Failure Handling[​](#failure-handling "Direct link to Failure Handling")

The whole pipeline is atomic with respect to the user operation:

-   If `sender` does not match the personal account, the call reverts with [`InvalidSender`](/smart-accounts/reference/IMasterAccountController#invalidsender).
-   If `nonce` is not the expected value, it reverts with [`InvalidNonce`](/smart-accounts/reference/IMasterAccountController#invalidnonce).
-   If the memo body has the wrong length for its instruction ID, it reverts with [`InvalidMemoData`](/smart-accounts/reference/IMasterAccountController#invalidmemodata); an unrecognized instruction byte reverts with [`InvalidInstructionId`](/smart-accounts/reference/IMasterAccountController#invalidinstructionid).
-   If any inner call reverts, the personal account surfaces it as [`CallFailed`](/smart-accounts/reference/IPersonalAccount#callfailed) and the entire user operation reverts.

Because the FXRP transfer is performed before the memo is decoded, **the mint succeeds even if the user operation reverts** - see [`DirectMintingExecuted`](/smart-accounts/reference/IMasterAccountController#directmintingexecuted). The freshly minted FXRP remains in the personal account, and the user can either re-submit a fixed user operation or transfer the FXRP to another address via standard [FAssets instructions](/smart-accounts/fasset-instructions).

## Next Steps[​](#next-steps "Direct link to Next Steps")

-   Walk through a Viem implementation in the [Raw Custom Instruction TypeScript guide](/smart-accounts/guides/typescript-viem/raw-custom-instruction-ts).
-   Read the [Custom Instruction](/smart-accounts/custom-instruction) for the recommended hash-commitment variant.
-   Compare the two flows in the [Custom Instruction Comparison](/smart-accounts/custom-instruction-comparison).
-   Dig into `IMasterAccountController` in the [reference](/smart-accounts/reference/IMasterAccountController).