Sign a userOperation for Paymaster sponsorization

Category: User Operations

Description: This endpoint streamlines gasless transactions by completing a partial ERC-4337 userOperation (missing paymasterAndData and signature). The INDID backend validates that the Paymaster is authorized to sponsor the operation, signs the userOperation by adding the Paymaster data, and locks the maximum estimated CU amount from the user's credit (with a refund if the actual cost is lower). It returns the userOperation with the signed paymasterAndData, ready to be forwarded to the Bundler so your app can pay gas fees on behalf of the end user.

Type: POST

URL: /sign-paymaster-op

Requirements

• A valid API Key must be provided (header Authorization: Bearer <API_KEY>)
• The provided chainId must be configured for the project
• The Account Abstraction module must be enabled for the project

Body Params (IUserOperation)

The userOperation must NOT include paymasterAndData and signature.

Name	Type	Description	Required?
sender	string	The address of the sender smart contract wallet	✅
nonce	bigNumberish	The nonce of the sender smart contract wallet	✅
initCode	bytesLike	The init code of the sender smart contract wallet	✅
callData	bytesLike	The data to be sent to the sender smart contract account during execution	✅
callGasLimit	bigNumberish	The gas limit for the execution of the callData	✅
verificationGasLimit	bigNumberish	The gas limit for the verification of the signature and the nonce of the userOperation	✅
preVerificationGas	bigNumberish	The gas limit for all the operations before the verification of the signature and the nonce of the userOperation	✅
maxFeePerGas	bigNumberish	The maximum fee per gas unit that can be paid by the userOperation	✅
maxPriorityFeePerGas	bigNumberish	The maximum priority fee per gas unit that can be paid by the userOperation	✅

Response

type SignPaymasterOpResponse = {
  paymasterAndData: string; // Signed paymaster data to include in the userOperation
};

Error Handling

HTTP Status	Meaning
200	OK
403	Unauthorized userOperation - validation failure
512	Internal server error while signing userOperation
515	Error during partial userOp parsing. Wrong input format for the partial userOp

Code Examples

Installation

npm i node-fetch

Request

data: IUserOperation;
const dataWithChainId = {
  ...data,
  chainid: this.chainId,
};

const url = `${this.backendUrl}/sign-paymaster-op`;
let config = {
  method: "post",
  maxBodyLength: Infinity,
  headers: {
    "Content-Type": "application/json",
    Authorization: `Bearer ${this.apiKey}`,
  },
  body: JSON.stringify(dataWithChainId),
};

const response = await fetch(url, config);
const JSONResponse = await response.json();