> ## Documentation Index > Fetch the complete documentation index at: https://docs.portalhq.io/llms.txt > Use this file to discover all available pages before exploring further. # Sign a transaction or message by chain > Signs a transaction or message using an RPC method and chain ID. The `Idempotency-Key` header is accepted only for broadcast methods (for example `eth_sendTransaction`, `sol_signAndSendTransaction`). Supplying the header with a non-broadcast method returns 400. ## OpenAPI ````yaml /openapi/enclave-mpc-api.yaml post /v1/sign openapi: 3.1.0 info: title: Portal Enclave MPC API version: '1.0' description: | The Enclave MPC API provides endpoints for MPC wallet generation, signing, backup, and recovery. All endpoints require a Client API Key or Client Session Token as a Bearer token. ## Base URL `https://mpc-client.portalhq.io` servers: - url: https://mpc-client.portalhq.io security: - bearerAuth: [] tags: - name: MPC Operations description: MPC wallet generation, signing, asset transfers, backup, and recovery paths: /v1/sign: post: tags: - MPC Operations summary: Sign a transaction or message by chain description: | Signs a transaction or message using an RPC method and chain ID. The `Idempotency-Key` header is accepted only for broadcast methods (for example `eth_sendTransaction`, `sol_signAndSendTransaction`). Supplying the header with a non-broadcast method returns 400. operationId: sign parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/SignRequest' example: share: eyJjbG... method: eth_sendTransaction params: value: '0x01' from: '' to: '0xdFd8302f44727A6348F702fF7B594f127dE3A902' data: '' rpcUrl: https://api.portalhq.io/rpc/v1/eip155/10143 chainId: eip155:10143 responses: '200': description: Signed successfully content: application/json: schema: $ref: '#/components/schemas/SignResponse' example: data: >- 0xf7a6a07fa599db56fca50fa1202670b59054e7ed452ea57b3f5b43148b8bdb165beb3a4b0fd532162a1f0fd475de1a9ecd07c95186f7a0856ce1bffa45e3acc91b '400': description: Bad request content: application/json: schema: $ref: '#/components/schemas/MpcErrorResponse' example: id: RPC_OP_FAILED message: 'Failed to send transaction: details' '401': description: Unauthorized content: text/plain: schema: type: string example: Incorrect API key format '404': description: >- Portal-managed presignature not found or not decryptable with the supplied share content: application/json: schema: $ref: '#/components/schemas/MpcErrorResponse' '409': description: Idempotent request already completed content: application/json: schema: $ref: '#/components/schemas/IdempotencyConflict' '422': description: Idempotency key reused with different payload content: application/json: schema: $ref: '#/components/schemas/IdempotencyReuse' components: parameters: IdempotencyKey: name: Idempotency-Key in: header required: false description: | A caller-provided key used for safe retries. Behavior depends on the endpoint: - **`POST /v1/presign/{curve}` with `managed: true`** — retrying a completed request with the same key returns the same `{id, expiresAt}` (200). If the original attempt is still in progress, the retry returns 409 with a `Retry-After` header; if the original attempt failed before completing, it returns 409 without `Retry-After` (caller should retry with a new key). Reusing a key after the wallet's signing share has changed (for example, after a reshare or recovery) returns 422. - **`POST /v1/sign`** — only honored for broadcast methods (for example `eth_sendTransaction`, `sol_signAndSendTransaction`). Supplying the header with a non-broadcast method returns 400. For broadcast methods, retrying a completed request returns 409 (`IDEMPOTENT_REQUEST_ALREADY_COMPLETED`), and reuse with a different payload returns 422. On 409, the response body does not include the original signing result — the header prevents double-execution, it does not replay the prior response. - **`POST /v1/assets/send`** — retrying a completed request returns 409 (`IDEMPOTENT_REQUEST_ALREADY_COMPLETED`), and reuse with a different payload returns 422. On 409, the response body does not include the original `transactionHash` — the header prevents double-submission, it does not replay the prior response. Client-stored presignature creation does not currently honor this header. schema: type: string schemas: SignRequest: type: object description: Request body for signing a transaction or message by chain. properties: method: type: string description: | The signer RPC method (e.g. `personal_sign`, `eth_sendTransaction`, `sol_signAndSendTransaction`). params: oneOf: - type: object - type: array description: | The parameters for the RPC method as a JSON object or array (e.g. `{"value": "0x01", "from": "", "to": "0x...", "data": ""}`). share: type: string description: The MPC share for the relevant curve. chainId: type: string description: The blockchain network as a CAIP-2 chain ID (e.g. `eip155:10143`). to: type: string description: The recipient's address. rpcUrl: type: string description: The node provider RPC URL. metadataStr: type: string description: Optional metadata string for the transaction. sponsorGas: type: boolean description: | Set to `false` to opt out of gas sponsorship for Account Abstraction clients. Defaults to `true` when omitted. presignature: type: string description: > The `data` value from a client-stored presign response. Omit for standard (non-presigned) signing. Mutually exclusive with `presignatureId`. presignatureId: type: string description: > The `id` value from a Portal-managed presign response. Omit for standard (non-presigned) signing. Mutually exclusive with `presignature`. required: - method - params - share - chainId - to - rpcUrl SignResponse: type: object description: Response containing the signed data. properties: data: type: string description: The signed data as a hex string. required: - data MpcErrorResponse: type: object description: Standard error response from the Enclave MPC API. properties: id: type: string description: >- Short error identifier (e.g. `DKG_FAILED`, `BAD_REQUEST`, `RPC_OP_FAILED`). message: type: string description: Human-readable error details. required: - id IdempotencyConflict: type: object description: >- Returned when the Idempotency-Key has already been used with an identical request body. properties: id: type: string example: IDEMPOTENT_REQUEST_ALREADY_COMPLETED message: type: string example: Request already completed required: - id - message IdempotencyReuse: type: object description: >- Returned when the Idempotency-Key has already been used with a different request body. properties: id: type: string example: IDEMPOTENCY_KEY_REUSED message: type: string example: Idempotency key reused for different request payload required: - id - message securitySchemes: bearerAuth: type: http scheme: bearer description: Client API Key or Client Session Token ````