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This guide walks you through the steps to fulfill and execute a trade from the maker side on StableFX.

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Prerequisites

Before you begin this quickstart, ensure you have:
  • Obtained an API key for StableFX from Circle
  • Set up a web3 provider or wallet that supports EIP-712 signatures
  • Granted a USDC allowance to the Permit2 contract. See How-to: Grant USDC Allowance to Permit2 for more information.
  • cURL installed on your development machine
This quickstart provides API request examples in cURL format, along with example responses.
StableFX uses a single endpoint for all API requests. The base URL is https://api.circle.com/. The StableFX API uses your API key for authentication and to determine which environment to use. The TEST environment executes against Arc testnet and returns mock data.When developing or testing your integration, you should use your TEST API key. When you are ready to move to production, just update your code to use your PROD API key.

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Part 1: Query for available trades

Query for trades with the confirmed status using the get trades endpoint. These are trades created by takers that are ready for maker fulfillment. 
curl --request GET \
  --url https://api.circle.com/v1/exchange/stablefx/trades?type=maker&status=confirmed \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer ${YOUR_API_KEY}'
Response 
{
  "data": [
    {
      "id": "c2558cd1-98b5-4ccd-90b8-96891512af20",
      "contractTradeId": "b4cdae0f-9285-48bf-8abf-109ae0177621",
      "status": "confirmed",
      "rate": "0.915",
      "from": {
        "currency": "USDC",
        "amount": "1000.00"
      },
      "to": {
        "currency": "EURC",
        "amount": "915.00"
      },
      "createDate": "2025-08-07T11:01:00Z",
      "updateDate": "2025-08-07T11:01:00Z",
      "quoteId": "c4d1da72-111e-4d52-bdbf-2e74a2d803d5"
    }
  ],
  "pagination": {
    "next": "",
    "previous": ""
  }
}

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Part 2: Select a trade to fulfill

Choose a trade from the available confirmed trades that you want to fulfill as a maker. You’ll need the trade ID for the subsequent steps.

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Part 3: Confirm trade intent

Confirm your trade intent through the StableFX API before submitting the trade on the blockchain.

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3.1. Generate maker signature data

To submit the trade onchain, you must first sign the trade intent with an EIP-712 signature. To get the data to sign, call the generate trade presign data endpoint. Your request must include the ID of the trade you want to fulfill. 
curl --request GET \
  --url https://api.circle.com/v1/exchange/stablefx/signatures/presign/maker/${stablefx_trade_id} \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer ${YOUR_API_KEY}'
Response 
{
  "consideration": {
    "quoteId": "c4d1da72-111e-4d52-bdbf-2e74a2d803d5",
    "base": "0x...",
    "quote": "0x...",
    "baseAmount": "100000000",
    "quoteAmount": "91500000",
    "maturity": 1752148800
  },
  "deadline": 1752149700,
  "fee": "100000"
}

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3.2. Sign the data

Using an EIP-712 compatible wallet or application, sign the data returned in the previous step.

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3.3. Submit the trade signature

Confirm your trade intent by submitting the signed data to the submit trade signature endpoint. This request must include the trade ID, the side of the trade that you are taking, the address of the wallet signing the payload, the data itself, and the signature on the data. 
curl --request POST \
  --url https://api.circle.com/v1/exchange/stablefx/signatures \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer ${YOUR_API_KEY}' \
  --header 'Content-Type: application/json' \
  --data '
{
  "tradeId": "${stablefx_trade_id}",
  "type": "maker",
  "address": "0xabc123...",
  "details": {
    "consideration": {
      "quoteId": "c4d1da72-111e-4d52-bdbf-2e74a2d803d5",
      "base": "0x...",
      "quote": "0x...",
      "baseAmount": "100000000",
      "quoteAmount": "91500000",
      "maturity": 1752148800
    },
    "deadline": 1752149700,
    "fee": "100000"
  },
  "signature": "0xsignature"
}
'
If the signed data is accepted, the API returns a blank 200 response.

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Part 4: Submit the funds onchain

Next, you need to deliver the funds onchain to complete the trade. The StableFX API can handle the onchain transaction for you using the Permit2 contract.

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4.1. Get the funding signature data

To use the StableFX API to deliver the funds onchain, you must first sign the funding typed data with an EIP-712 signature. To get the data to sign, call the generate funding presign data endpoint. Your request must include the contract ID of the trade and the side of the trade that you are taking. The following an example request: 
curl --request POST \
  --url https://api.circle.com/v1/exchange/stablefx/signatures/funding/presign \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer ${YOUR_API_KEY}' \
  --header 'Content-Type: application/json' \
  --data '
{
  "contractTradeIds": ["${stablefx_trade_id}"],
  "type": "maker"
}
'
Response 
{
  "typedData": {
    "domain": {
      "name": "Permit2",
      "chainId": 11155111,
      "verifyingContract": "0xffd21ca8F0876DaFAD7de09404E0c1f868bbf1AE"
    },
    "types": {
      "EIP712Domain": [
        {
          "name": "name",
          "type": "string"
        },

        {
          "name": "chainId",
          "type": "uint256"
        },

        {
          "name": "verifyingContract",
          "type": "address"
        }
      ],
      "TokenPermissions": [
        {
          "name": "token",
          "type": "address"
        },

        {
          "name": "amount",
          "type": "uint256"
        }
      ],
      "SingleTradeWitness": [
        {
          "name": "id",
          "type": "uint256"
        }
      ],
      "PermitWitnessTransferFrom": [
        {
          "name": "permitted",
          "type": "TokenPermissions"
        },

        {
          "name": "spender",
          "type": "address"
        },

        {
          "name": "nonce",
          "type": "uint256"
        },

        {
          "name": "deadline",
          "type": "uint256"
        },

        {
          "name": "witness",
          "type": "SingleTradeWitness"
        }
      ]
    },
    "primaryType": "PermitWitnessTransferFrom",
    "message": {
      "permitted": {
        "token": "0xTOKEN",
        "amount": "1000"
      },
      "spender": "0xffd21ca8F0876DaFAD7de09404E0c1f868bbf1AE",
      "nonce": "42",
      "deadline": "1735689600",
      "witness": {
        "id": "10"
      }
    }
  }
}

​
4.2. Sign the funding data

Using a Permit2-compliant EIP-712 compatible wallet or application, sign the data returned in the previous step.

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4.3. Submit the funding signature

To deliver the funds onchain, you must submit the maker-specific Permit2 data along with your signature to the fund trade endpoint. The endpoint allows you to submit either a single object or a batch of objects along with the required signatures. The following is an example request for a single trade: 
curl --request POST \
  --url https://api.circle.com/v1/exchange/stablefx/fund \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer ${YOUR_API_KEY}' \
  --header 'Content-Type: application/json' \
  --data '
{
  "type": "maker",
  "signature": "0xsignature",
  "permit2": {
    "permitted": {
      "token": "0xTOKEN1",
      "amount": "915"
    },
    "spender": "0xTOKEN1",
    "nonce": "123456",
    "deadline": 1752149700,
    "witness": {
      "id": "123456"
    }
  }
}
'
If the signed data is accepted, the API returns a blank 200 response.
Note: It’s not required to submit the funding transaction through the StableFX API. You can submit the transaction onchain using your own web3 provider or wallet by calling the appropriate maker contract methods directly.