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Introduction

This guide will show you how to quickly buy or sell any tokenized asset (NFT) with USDC, using Crossmint’s headless APIs.

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Prerequisites

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From Crossmint

  1. Create a developer account in the Staging Console.
  2. Create a new collection or import yours into the console, and have your collectionId ready.
    • Make sure you follow the maximum prices for collections set in staging outlined here.
  3. Create a server-side API key with the orders.create, orders.update, and orders.read scopes enabled. More info on creating API keys here.
This Quickstart assumes that you'll be using the API Playground or cURL requests to make the API calls. This approach requires the use of a server-side API key.If you would rather follow the quickstart while building a client-side app that makes requests to Crossmint directly from the browser, you must use a client-side API key. See the Server or Client Guide for more information.
To integrate in production/mainnet, you'll also need to complete account and collection verification. More information in the production launch guide.

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External prerequisites

Wallet

Crypto wallet supporting USDC - Metamask, Phantom, Coinbase Wallet, etc.

Testnet Balance

A small balance of USDC testnet currency in your wallet on the Base-sepolia network.Get testnet USDC here:
The above faucet provides both USDC and USDXM. This quickstart uses USDC by default, but you can also use USDXM (see contract address below).
USDXM is a test token that represents USDC. It has the same behavior as USDC. In production, you’ll use real USDC instead.
Adding USDC to MetaMask:
  • Import the token to MetaMask:
    1. Open MetaMask and click “Import tokens”
    2. For USDC: Use the official USDC contract address from Circle 0x036CbD53842c5426634e7929541eC2318f3dCF7e
    3. For USDXM: Use the USDXM contract address 0x14196F08a4Fa0B66B7331bC40dd6bCd8A1dEeA9F
    4. Click Import
    5. Refresh your wallet

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Create an order and pay with USDC

1

Setup your Python environment

Clone the quickstart repo:
git clone https://github.com/crossmint/headless-python-payusdc.git
Navigate to the project directory and create a virtual environment:
cd headless-python-payusdc
python3 -m venv .venv
source .venv/bin/activate
Install the dependencies:
pip install -r requirements.txt
2

Set keys in .env

Set the following keys in the .env file:
CROSSMINT_API_KEY="<your-api-key>"
COLLECTION_ID="<your-collection-id>"
PAYER_ADDRESS="<your-payer-address>"
EMAIL_ADDRESS="<your-email-address>"
  • CROSSMINT_API_KEY, COLLECTION_ID are found from the Developer Console. See Prerequisites
  • PAYER_ADDRESS is your wallet address that contains USDC.
  • EMAIL_ADDRESS is where you’ll receive your NFT in a new Crossmint wallet that you can access later.
3

Create order with USDC payment

Run the application:
python src/index.py
This will:
  1. Create an order that is waiting for a USDC payment on the Base-sepolia network
  2. Return the serializedTransaction, which will be used in the next step
  3. Poll the status of the order until it is complete
Serialized transaction
4

Receive Payment

  1. Copy the serializedTransaction returned in the previous step and paste it below
  2. Connect to your USDC wallet that was specified in the .env file
  3. Send the transaction
5

Status of order

The code will poll for the status of the order until it is marked as complete. You should see it changing from “payment” to “delivery” and finally to “completed”.
You will also see the final order details, including the transaction hash, in your terminal.
Order status

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Access your NFT

Once the order is complete, you will receive an email with a link to the purchased item, which can be viewed in the Crossmint website.
You can also access your NFT by logging in to your Crossmint wallet at crossmint.com with the email address you specified in the .env file.

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Understanding the code

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Creating an order

The order creation process involves sending a POST request to Crossmint’s API with the necessary payment and recipient details. Let’s break down the key components:
src/create_order.py
def create_order():
    # Define the order data structure
    order_data = {
        "recipient": {
            "email": os.environ.get("EMAIL_ADDRESS")  # Email where the NFT will be delivered
        },
        "locale": "en-US",  # Language/region setting
        "payment": {
            "method": "base-sepolia",  # Testnet network for USDC payments
            "currency": "usdc",            # Payment currency
            "payerAddress": os.environ.get("PAYER_ADDRESS")  # Wallet address paying USDC
        },
        "lineItems": {
            "collectionLocator": f"crossmint:{os.environ.get('COLLECTION_ID')}"  # Tokenized collection identifier
        }
    }

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Key parameters explained

  • recipient: Specifies where to deliver the tokenized asset
    • email: The email address where the tokenized asset will be delivered in a Crossmint wallet. Instead of an email, a walletAddress field can be used to deliver the asset to a specific wallet address.
  • payment: Defines how the payment will be made
    • method: The blockchain network (base-sepolia for testnet)
    • currency: The payment currency (usdc)
    • payerAddress: The wallet address that will send the USDC payment
  • lineItems: Specifies what is being purchased
    • collectionLocator: Identifies the collection

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API request

src/create_order.py
    response = requests.post(
        f"{base_url}/orders",
        headers={
            "Content-Type": "application/json",
            "x-api-key": os.environ.get("CROSSMINT_API_KEY")  # Your API key for authentication
        },
        json=order_data
    )
The API request:
  • Sends a POST request to Crossmint’s order endpoint
  • Includes your API key for authentication
  • Sends the order data as JSON in the request body

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Response handling

src/create_order.py
    validate(response.ok, f"Failed to create order: {response.reason}")
    json_response = response.json()
    return {
        "clientSecret": json_response["clientSecret"],  # Used for order authentication
        "order": json_response["order"]                 # Contains order details
    }
The response includes:
  • clientSecret: A unique token used for authenticating subsequent requests for this order
  • order: The order details including the order ID and status
For more details on creating orders via the headless API, see the Create Order API Reference.

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Polling an order

The order status polling process involves periodically checking the order’s status until it’s completed. Let’s examine how this works:
src/get_order.py
def get_order(order_id: str, client_secret: str) -> Dict[str, Any]:
    try:
        response = requests.get(
            f"{base_url}/orders/{order_id}",  # Endpoint for specific order
            headers={
                'Content-Type': 'application/json',
                'x-api-key': os.environ.get('CROSSMINT_API_KEY'),  # API authentication
                'Authorization': client_secret                      # Order-specific authentication
            }
        )

        validate(response.ok, f"Failed to get order: {response.reason}")
        return response.json()
    except Exception as error:
        raise error

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Get order function explained

  • Takes order_id and client_secret as parameters
  • Makes a GET request to fetch the current state of the order
  • Uses both API key and client secret for authentication
  • Returns the order details as JSON
src/get_order.py
def poll_order(order_id: str, client_secret: str) -> Dict[str, Any]:
    while True:
        try:
            order = get_order(order_id, client_secret)
            print(f'Current order status: [bold yellow]{order["phase"]}[/bold yellow]')

            if order['phase'] == 'completed':
                return order
            time.sleep(3)  # Wait 3 seconds before next check

        except Exception as error:
            raise error

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Poll order function explained

  • Continuously checks the order status every 3 seconds.
  • Prints the current phase of the order
  • Possible order phases include:
    • payment: Waiting for or processing payment
    • delivery: NFT is being delivered
    • completed: Order is successfully completed
  • Returns the final order details when completed
The 3-second polling interval helps prevent rate limiting while still providing timely updates. Adjust this value based on your needs. For more details on polling for order status, see the Get Order API Reference.
Always implement proper error handling, retry mechanisms, and asynchronous polling in production environments to handle network issues or API interruptions.