Getting Started

Prerequisites

Before using the SDK, you'll need:

API Credentials - Client ID and Client Secret from the Partner Dashboard (for your backend)
A backend endpoint - To generate checkout tokens for your frontend
Invoice ID - The invoice the customer will be paying
A container element - An HTML element where the SDK will render

Important: API credentials (Client ID and Secret) should only be used on your backend server. The frontend SDK uses access tokens generated by your backend to keep credentials secure.

Step-by-Step Setup

Install the SDK

npm install @getalternative/partner-sdk

Create a Backend Token Endpoint

Your backend generates checkout tokens using your API credentials:

// backend/routes/checkout.ts (example with Express)
import express from 'express';

const router = express.Router();

router.post('/api/checkout-token', async (req, res) => {
  const { customerId, invoiceId } = req.body;

  // 1. Get OAuth token using client credentials
  const oauthResponse = await fetch('https://public-api.alternativepayments.io/oauth/token', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded',
      'Authorization': `Basic ${Buffer.from(`${CLIENT_ID}:${CLIENT_SECRET}`).toString('base64')}`,
    },
    body: 'grant_type=client_credentials',
  });
  const { access_token } = await oauthResponse.json();

  // 2. Generate checkout token
  const checkoutResponse = await fetch('https://public-api.alternativepayments.io/v1/checkout-auth/init', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${access_token}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ customer_id: customerId, invoice_id: invoiceId }),
  });
  const { token, expires_at } = await checkoutResponse.json();

  res.json({ token, expiresAt: expires_at });
});

Add a Container Element

<div id="payment-container"></div>

Initialize the SDK

import { AlternativeClient } from '@getalternative/partner-sdk';

// Fetch token from your backend
const { token } = await fetch('/api/checkout-token', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ customerId: 'cus_xxx', invoiceId: 'inv_xxx' }),
}).then(res => res.json());

// Initialize SDK
const client = await AlternativeClient.create({
  accessToken: token,
  environment: 'production',
  onAccessTokenExpired: async () => {
    // Re-fetch token when expired
    const response = await fetch('/api/checkout-token', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ customerId: 'cus_xxx', invoiceId: 'inv_xxx' }),
    });
    const { token } = await response.json();
    return token;
  },
});

Create the Payment Flow

const flow = client.createPaymentFlow({
  containerId: 'payment-container',
  onPaymentSuccess: (payment) => {
    console.log('Payment completed:', payment.id);
  },
  onPaymentError: (error) => {
    console.error('Payment failed:', error.message);
  },
});

Configuration Options

AlternativeClientConfig

Property

Type

Required

Description

accessToken

string

Yes

JWT access token from your backend

environment

'production' | 'staging'

API environment (default: production)

baseUrl

string

Custom API base URL (overrides environment)

timeout

number

Request timeout in ms (default: 30000)

retries

number

Number of retry attempts (default: 3)

onAccessTokenExpired

() => Promise<string>

Callback to fetch new token when expired

theme

ThemeConfig

Default theme for all components

Environments

Environment

Description

production

Live environment for real payments

staging

Test environment for development

Important: Use separate API credentials for each environment. Production credentials will not work in staging and vice versa.

Full Example

<!DOCTYPE html>
<html>
<head>
  <title>Payment Page</title>
</head>
<body>
  <h1>Complete Your Payment</h1>
  <div id="payment-container"></div>

  <script type="module">
    import { AlternativeClient } from '@getalternative/partner-sdk';

    // Fetch token from your backend
    const { token } = await fetch('/api/checkout-token', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        customerId: 'cus_abc123',
        invoiceId: 'inv_abc123'
      }),
    }).then(res => res.json());

    const client = await AlternativeClient.create({
      accessToken: token,
      environment: 'staging',
      onAccessTokenExpired: async () => {
        const response = await fetch('/api/checkout-token', {
          method: 'POST',
          headers: { 'Content-Type': 'application/json' },
          body: JSON.stringify({
            customerId: 'cus_abc123',
            invoiceId: 'inv_abc123'
          }),
        });
        const { token } = await response.json();
        return token;
      },
    });

    const flow = client.createPaymentFlow({
      containerId: 'payment-container',
      onPaymentSuccess: (payment) => {
        alert('Payment successful!');
        window.location.href = '/thank-you';
      },
      onPaymentError: (error) => {
        alert('Payment failed: ' + error.message);
      },
      onClose: () => {
        console.log('Payment flow closed');
      },
    });

    // Cleanup when navigating away
    window.addEventListener('beforeunload', () => {
      flow.unmount();
    });
  </script>
</body>
</html>

React Integration

import { useEffect, useRef } from 'react';
import { AlternativeClient } from '@getalternative/partner-sdk';

interface PaymentWidgetProps {
  customerId: string;
  invoiceId: string;
}

function PaymentWidget({ customerId, invoiceId }: PaymentWidgetProps) {
  const flowRef = useRef<ReturnType<typeof AlternativeClient.prototype.createPaymentFlow> | null>(null);

  useEffect(() => {
    let mounted = true;

    async function initPayment() {
      // Fetch token from your backend
      const { token } = await fetch('/api/checkout-token', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ customerId, invoiceId }),
      }).then(res => res.json());

      if (!mounted) return;

      const client = await AlternativeClient.create({
        accessToken: token,
        environment: 'staging',
        onAccessTokenExpired: async () => {
          const response = await fetch('/api/checkout-token', {
            method: 'POST',
            headers: { 'Content-Type': 'application/json' },
            body: JSON.stringify({ customerId, invoiceId }),
          });
          const { token } = await response.json();
          return token;
        },
      });

      if (!mounted) return;

      flowRef.current = client.createPaymentFlow({
        containerId: 'payment-container',
        onPaymentSuccess: (payment) => {
          console.log('Success:', payment);
        },
      });
    }

    initPayment();

    return () => {
      mounted = false;
      flowRef.current?.unmount();
    };
  }, [customerId, invoiceId]);

  return <div id="payment-container" />;
}

Next Steps

Authentication Payment Flow Theming

PreviousAuthentication NextPayment Flow

Last updated 16 days ago

Was this helpful?