FlexSub SDK

⚡ Cross-chain Subscription SDK for Web3

Add flexible subscription payments to any dApp with one SDK.
Users pay from any chain. Merchants receive USDC.

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📦 What is FlexSub SDK?

FlexSub SDK is a TypeScript library that enables developers to integrate subscription payments into their Web3 applications. It abstracts away the complexity of cross-chain transactions, micropayments, and stablecoin settlements.

import { FlexSub, YellowIntegration, LiFiIntegration, ArcIntegration } from '@flexsub/sdk';

// Initialize with your preferred payment method
const flexsub = new FlexSub({
  arc: new ArcIntegration({ usdcAddress, contractAddress }),
  lifi: new LiFiIntegration({ targetChain: 'arbitrum' }),
  yellow: new YellowIntegration({ clearNodeUrl: 'wss://clearnet.yellow.com/ws' })
});

// Create a subscription
await flexsub.subscribe({ planId: 1, paymentMethod: 'arc' });

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💡 Why FlexSub?

The Problem

• Chain Fragmentation: Users have assets on multiple chains
• Gas Fee Overhead: Every payment incurs gas fees
• Stablecoin Friction: Merchants want USDC, users hold various tokens

Our Solution

Feature	How
Pay from Anywhere	LI.FI bridges any token → USDC
Instant & Gas-less	Yellow Network state channels
Stable Settlement	Circle USDC on-chain

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🎬 Demo

Subscription Dashboard showing active subscription via Yellow Micropayment

👉 Try Live Demo

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🛠️ SDK Modules

@flexsub/sdk/arc - USDC Settlement

import { ArcIntegration } from '@flexsub/sdk';

const arc = new ArcIntegration({
  usdcAddress: '0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d',
  contractAddress: '0xE5074CBbd046AFb491EB8692abD6cF7ECCC6dEE5'
});

await arc.approveUSDC(amount);
await arc.subscribe(planId);

@flexsub/sdk/lifi - Cross-Chain

import { LiFiIntegration } from '@flexsub/sdk';

const lifi = new LiFiIntegration({ integrator: 'your-app' });

const quote = await lifi.getQuote({
  fromChain: 137,        // Polygon
  toChain: 42161,        // Arbitrum
  fromToken: 'MATIC',
  toToken: 'USDC',
  amount: '10'
});

@flexsub/sdk/yellow - Micropayments

import { YellowIntegration } from '@flexsub/sdk';

const yellow = new YellowIntegration({
  clearNodeUrl: 'wss://clearnet-sandbox.yellow.com/ws'
});

await yellow.connect();
await yellow.openChannel(depositAmount);
await yellow.sendPayment(0.001); // Instant, no gas!
await yellow.closeChannel();

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📁 Project Structure

flexsub/
├── sdk/              ← 🌟 Core SDK
│   ├── src/arc.ts       # USDC settlement
│   ├── src/lifi.ts      # Cross-chain bridge
│   └── src/yellow.ts    # Micropayments
│
├── contracts/        ← Smart Contracts
│   └── src/FlexSubManager.sol
│
└── demo/             ← Demo Website

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🚀 Quick Start

# Install SDK
pnpm add @flexsub/sdk

# Or clone the repo
git clone https://github.com/UranusLin/flexsub.git
cd flexsub
pnpm install
pnpm build

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🔗 Deployment

Network	Contract	Address
Arbitrum Sepolia	FlexSubManager	0xE5074CBbd046AFb491EB8692abD6cF7ECCC6dEE5
Arbitrum Sepolia	USDC (Circle)	0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d

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📄 License

MIT