> ## Documentation Index > Fetch the complete documentation index at: https://docs.getpara.com/llms.txt > Use this file to discover all available pages before exploring further. # Sign Transaction > Sign a transaction with a wallet's private key share via MPC. **EVM:** Provide unsigned transaction fields as a JSON object and the endpoint will RLP-encode them, sign via MPC, and return a fully serialized signed transaction (hex-encoded with `0x` prefix) ready for broadcast. **Solana:** Provide a base64-encoded serialized Solana transaction (as built by `@solana/web3.js`). Both legacy `Transaction` and versioned `VersionedTransaction` (v0, with Address Lookup Tables) are accepted; the endpoint auto-detects the format, signs via MPC, and returns the signed transaction as a base64 string ready for broadcast. Set top-level `broadcast: true` to broadcast the signed transaction for EVM or Solana wallets. Broadcasted calls create a persisted transaction record, return `txHash` and `transactionId`, and set `x-transaction-id`. Omitted `broadcast` remains sign-only and writes no transaction-history row. Stellar wallets do not support `broadcast: true`. **Stellar:** Provide a base64-encoded Stellar transaction envelope (XDR) in the `transaction` field and the network passphrase in `networkPassphrase`. The endpoint computes the transaction hash, signs it via MPC, and returns the signed transaction as a base64-encoded XDR string. ## OpenAPI ````yaml /openapi.yaml post /v1/wallets/{walletId}/sign-transaction openapi: 3.0.3 info: title: Para REST API version: '1.0' description: Server-to-server wallet creation and signing over HTTP servers: - url: https://api.beta.getpara.com description: Beta - url: https://api.getpara.com description: Production security: - ApiKeyAuth: [] paths: /v1/wallets/{walletId}/sign-transaction: post: tags: - Signing summary: Sign Transaction description: > Sign a transaction with a wallet's private key share via MPC. **EVM:** Provide unsigned transaction fields as a JSON object and the endpoint will RLP-encode them, sign via MPC, and return a fully serialized signed transaction (hex-encoded with `0x` prefix) ready for broadcast. **Solana:** Provide a base64-encoded serialized Solana transaction (as built by `@solana/web3.js`). Both legacy `Transaction` and versioned `VersionedTransaction` (v0, with Address Lookup Tables) are accepted; the endpoint auto-detects the format, signs via MPC, and returns the signed transaction as a base64 string ready for broadcast. Set top-level `broadcast: true` to broadcast the signed transaction for EVM or Solana wallets. Broadcasted calls create a persisted transaction record, return `txHash` and `transactionId`, and set `x-transaction-id`. Omitted `broadcast` remains sign-only and writes no transaction-history row. Stellar wallets do not support `broadcast: true`. **Stellar:** Provide a base64-encoded Stellar transaction envelope (XDR) in the `transaction` field and the network passphrase in `networkPassphrase`. The endpoint computes the transaction hash, signs it via MPC, and returns the signed transaction as a base64-encoded XDR string. operationId: signTransaction parameters: - $ref: '#/components/parameters/WalletId' - $ref: '#/components/parameters/RequestId' - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/SignTransactionRequest' responses: '200': description: Signed transaction headers: x-transaction-id: schema: type: string format: uuid description: >- Present only when `broadcast: true` created a persisted transaction record. content: application/json: schema: $ref: '#/components/schemas/SignTransactionResponse' '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '403': description: | Forbidden. Either the API key is invalid (`FORBIDDEN`) or a policy denied the operation (`POLICY_DENIED`). content: application/json: schema: oneOf: - $ref: '#/components/schemas/Error' - $ref: '#/components/schemas/PolicyDeniedError' examples: forbidden: summary: Invalid API key value: code: FORBIDDEN message: invalid secret api key policyDenied: summary: Denied by policy value: code: POLICY_DENIED message: Transaction denied by policy deniedBy: scopeName: transfers permissionType: TRANSFER '404': $ref: '#/components/responses/NotFound' '409': $ref: '#/components/responses/IdempotencyConflict' '422': $ref: '#/components/responses/Unprocessable' '429': $ref: '#/components/responses/TooManyRequests' '500': $ref: '#/components/responses/ServerError' components: parameters: WalletId: name: walletId in: path required: true description: Wallet ID schema: type: string example: 0a1b2c3d-4e5f-6789-abcd-ef0123456789 RequestId: name: X-Request-Id in: header required: false description: UUID for request tracing. Para returns one if omitted. schema: type: string format: uuid IdempotencyKey: name: Idempotency-Key in: header required: false description: > Unique key for safe retries on POST endpoints. If a request with the same key is received within 24 hours, the original response is returned without re-executing. Recommended format: UUID v4. Max length 256 characters. Returns 422 if the same key is reused with a different request body. Returns 409 if a request with the same key is still being processed. schema: type: string maxLength: 256 schemas: SignTransactionRequest: type: object required: - transaction properties: transaction: description: > EVM: JSON object with unsigned transaction fields. Solana: base64-encoded serialized transaction string. Stellar: base64-encoded XDR transaction envelope string. The API differentiates by the wallet's type (determined by `walletId`). Objects are treated as EVM transactions; strings are treated as Solana or Stellar transactions depending on the wallet type. For Stellar wallets, `networkPassphrase` is required. oneOf: - $ref: '#/components/schemas/EvmTransaction' - type: string description: >- Base64-encoded serialized Solana transaction. Accepts both legacy (`Transaction.serialize()`) and versioned (`VersionedTransaction.serialize()`, v0) formats, auto-detected on the server. example: AQAAAA... - type: string description: >- Base64-encoded Stellar transaction envelope (XDR). Must also provide `networkPassphrase`. example: AAAAAgAAAA... networkPassphrase: type: string description: >- Stellar network passphrase. Required when the wallet referenced by `walletId` is a STELLAR wallet. Ignored for other wallet types. example: Public Global Stellar Network ; September 2015 network: type: string enum: - SOLANA - SOLANA_DEVNET description: >- Solana network to broadcast to when `broadcast: true`. Uses the same environment rules as `POST /transfer`. broadcast: type: boolean default: false description: >- When true, broadcast the signed EVM or Solana transaction, create a persisted transaction record, and return `txHash` plus `transactionId`. Omitted or false remains sign-only. Stellar wallets reject `broadcast: true`. SignTransactionResponse: type: object required: - signedTransaction properties: signedTransaction: type: string description: >- Signed transaction ready for broadcast. EVM: RLP-encoded hex string with `0x` prefix. Solana: base64-encoded string. Stellar: base64-encoded XDR string. example: 0x02f8... txHash: type: string description: 'Transaction hash. Present only when `broadcast: true` succeeds.' example: 0x1234abcd... transactionId: type: string format: uuid description: >- Persisted transaction record id. Present only when `broadcast: true` creates a transaction-history row. example: 550e8400-e29b-41d4-a716-446655440000 Error: type: object required: - code - message properties: code: type: string description: Machine-readable error code for programmatic handling example: INVALID_REQUEST message: type: string description: Human-readable error message transactionId: type: string format: uuid description: >- Persisted transaction record id. Present only when a broadcast request failed after a history row was created. failureStage: type: string enum: - mpc_sign - signature_apply - signer_verify - broadcast - monitor_timeout description: >- Which stage of the broadcast lifecycle failed. Present on persisted broadcast failures. failureCode: type: string description: >- Machine-readable failure reason from the underlying broadcast helper (e.g. `INSUFFICIENT_NATIVE_BALANCE`, `EXECUTION_FAILED`). Present on broadcast-stage failures. signedTransaction: type: string description: >- Signed transaction bytes. Present on broadcast failures that happen after signing completed. additionalProperties: true description: > All error responses include `code` and `message` fields. Some errors include extra fields (e.g. `walletId` on 409 Conflict). Broadcast failures that occur after a persisted transaction row is created include `transactionId`, `failureStage`, and (on broadcast-stage failures) `failureCode`, and also set the `x-transaction-id` response header. If signing completed before the failure, `signedTransaction` is included so callers can inspect or retry the already-signed bytes. Common error codes: `INVALID_REQUEST`, `UNAUTHORIZED`, `FORBIDDEN`, `NOT_FOUND`, `CONFLICT`, `WALLET_ALREADY_EXISTS`, `WALLET_ALREADY_CLAIMED`, `RATE_LIMITED`, `INTERNAL_ERROR`. PolicyDeniedError: type: object properties: code: type: string example: POLICY_DENIED message: type: string example: Transaction denied by policy deniedBy: type: object properties: scopeName: type: string permissionType: type: string condition: type: object properties: resource: type: string comparator: type: string reference: {} EvmTransaction: type: object required: - to - chainId - type properties: to: type: string description: Destination address (contract deployment not supported) example: 0x742d35Cc6634C0532925a3b844Bc9e7595f... value: type: string description: Value in wei (decimal or 0x-prefixed hex) example: '0x2386f26fc10000' chainId: oneOf: - type: string - type: integer description: Chain ID (decimal or 0x-prefixed hex, e.g. "1" for Ethereum mainnet) example: '1' data: type: string description: Hex-encoded calldata (0x-prefixed) nonce: type: integer minimum: 0 description: Transaction nonce gasLimit: type: string description: Gas limit (decimal or 0x-prefixed hex) example: '0x5208' maxFeePerGas: type: string description: EIP-1559 max fee per gas (decimal or 0x-prefixed hex) maxPriorityFeePerGas: type: string description: EIP-1559 max priority fee per gas (decimal or 0x-prefixed hex) gasPrice: type: string description: Legacy gas price (decimal or 0x-prefixed hex) type: type: integer enum: - 0 - 2 description: 'Transaction type: 0 (legacy) or 2 (EIP-1559)' responses: BadRequest: description: Invalid request body content: application/json: schema: $ref: '#/components/schemas/Error' example: code: INVALID_REQUEST message: type must be one of EVM, SOLANA, COSMOS, STELLAR Unauthorized: description: API key not provided content: application/json: schema: $ref: '#/components/schemas/Error' example: code: UNAUTHORIZED message: secret api key not provided NotFound: description: Wallet not found content: application/json: schema: $ref: '#/components/schemas/Error' example: code: NOT_FOUND message: wallet not found IdempotencyConflict: description: A request with this idempotency key is currently being processed content: application/json: schema: $ref: '#/components/schemas/Error' example: code: CONFLICT message: A request with this idempotency key is currently being processed Unprocessable: description: Idempotency key reused with a different request body content: application/json: schema: $ref: '#/components/schemas/Error' example: code: UNPROCESSABLE message: >- Idempotency key has already been used with different request parameters TooManyRequests: description: Rate limit exceeded headers: Retry-After: schema: type: integer description: Seconds until the rate limit window resets example: 60 content: application/json: schema: $ref: '#/components/schemas/Error' example: code: RATE_LIMITED message: Rate limit exceeded, try again shortly. ServerError: description: Internal server error content: application/json: schema: $ref: '#/components/schemas/Error' example: code: INTERNAL_ERROR message: Internal Server Error securitySchemes: ApiKeyAuth: type: apiKey in: header name: X-API-Key description: Your partner secret key (server-side only) x-default: sk_your_secret_key_here ````