Docs / Web3 System / Core Concepts / Smart Contracts

📝 Smart Contracts

Explore the smart contract architecture that handles payments and PNPL.

📋 Contract Overview

Merso uses a set of audited smart contracts to handle payment processing, NFT escrow, and PNPL payment schedules on-chain.

💰

Payment Router

Routes payments to the correct destination and handles fee distribution.

🔒

Escrow Contract

Holds NFTs during PNPL payment periods until full payment is complete.

📅

Payment Schedule

Manages PNPL installment tracking and automatic payment collection.

⛓️ EVM Contracts

Contract Purpose Standard
MersoPaymentRouter Main entry point for all payments Custom
MersoEscrow NFT escrow for PNPL ERC-721 Receiver
MersoPNPL Payment schedule management Custom
TokenApproval ERC-20 approval helper ERC-20
🔍 Contract Verification

All Merso contracts are verified on block explorers. Contact us for specific contract addresses on your target chain.

📅 PNPL Smart Contract Flow

1
Initial Payment
User pays 25%
→
2
NFT to Escrow
Contract holds NFT
→
3
Weekly Payments
Auto-collected
→
4
Transfer
NFT to user
Solidity Interface 
interface IMersoPNPL {
    // Initialize a PNPL payment plan
    function initiatePlan(
        address buyer,
        address nftContract,
        uint256 tokenId,
        uint256 totalAmount,
        uint8 installments
    ) external returns (uint256 planId);

    // Process a weekly payment
    function processPayment(uint256 planId) external;

    // Get plan status
    function getPlanStatus(uint256 planId) 
        external view returns (
            uint256 paid,
            uint256 remaining,
            uint8 completedInstallments
        );
}

✅ Token Approval Process

Before making payments with ERC-20 tokens, users must approve the Payment Router contract to spend tokens on their behalf.

JavaScript 
// Step 1: Get approval transaction from Merso API
const approvalData = await fetch('/api/approval', {
    method: 'POST',
    body: JSON.stringify({
        token: 'USDC',
        amount: '100000000', // 100 USDC (6 decimals)
        chain_id: '137'
    })
});

// Step 2: User signs the approval transaction
const txHash = await wallet.sendTransaction(approvalData.transaction);

// Step 3: Wait for confirmation
await provider.waitForTransaction(txHash);
⚠️ Approval Best Practice

For security, we recommend approving only the exact amount needed rather than unlimited approvals. The Merso API generates minimal approval transactions by default.

☀️ Solana Programs

On Solana, Merso uses native programs for payment processing with the same functionality as EVM contracts.

Program Purpose
merso_payment Payment routing and fee distribution
merso_escrow NFT escrow using PDAs
merso_pnpl Payment schedule with SPL Token support

⛽ Gas Optimization

  • ✓
    Batched Operations
    Multiple operations combined into single transactions where possible.
  • ✓
    Efficient Storage
    Packed storage layouts minimize on-chain storage costs.
  • ✓
    Gas Estimation
    API provides accurate gas estimates before transaction submission.