Payment Processor Exchange Integration Generator

Project Setup

Before generating code, check the user’s project is configured:

1. Foundry: foundry.toml must exist. If not: forge init
2. Payment Processor (optional): forge install limitbreakinc/payment-processor for direct interface imports. Otherwise, scripts use inline interface definitions with the deployed contract addresses.
3. Local testing: For local development, use apptoken-dev to bootstrap an Anvil node with all Apptoken protocols at their deterministic addresses – see apptoken-general/references/project-setup.md.

Instructions

1. Parse the exchange integration requirements from $ARGUMENTS.
2. Resolve ambiguities before generating – if $ARGUMENTS mentions specific collections or tokens without addresses, or the order type (listing vs offer, standard vs PermitC, single vs bulk) isn’t clear from context, ask in a single message. If clear, proceed.
3. Determine the order types needed:
   • Listings (single, bulk, sweep)
   • Item offers
   • Collection offers
   • Token set offers
   • Bulk orders (merkle tree signing)
   • Partial fills (ERC1155)
4. Generate integration code covering:
   • EIP-712 order signing with the correct typehash
   • Calldata encoding via the PaymentProcessorEncoder at 0x9A1D00C3a699f491037745393a0592AC6b62421D
   • Proper struct construction for Order, SweepOrder, AdvancedOrder, etc.
5. Handle advanced features as needed:
   • Cosigner security: Short-lived cosignatures for order-book protection
   • PermitC: Time-bound approvals without setApprovalForAll
   • Bulk orders: Merkle tree signing for 2-1024 orders in a single signature
   • Partial fills: ERC1155 orders with requestedFillAmount and minimumFillAmount
6. Key detail: All trade functions on PaymentProcessor accept a single bytes calldata data parameter. This calldata is produced by the Encoder contract (called off-chain or on-chain).
7. The executor (msg.sender on PaymentProcessor) is always the taker of the trade.

Reference Files

• references/order-signing.md – EIP-712 signing, typehashes, nonces, and bulk orders
• references/order-filling.md – Trade function reference, calldata encoding, cancellation, and read-only functions
• references/permitc-integration.md – PermitC integration for time-bound approvals
• Protocol knowledge: payment-processor-protocol

Common Mistakes

• beneficiary for listings must be the buyer – For listings, beneficiary determines who receives the NFT and is set at fill time (it is NOT part of the signed SaleApproval typehash). Setting it to the seller’s address causes the NFT to transfer back to the seller. For offers, beneficiary IS signed by the buyer and determines where the NFT goes.
• revokeMasterNonce() is called directly on PaymentProcessor with no parameters and no encoder – it increments the caller’s nonce by 1, invalidating ALL previously signed orders
• Cosigned orders (nonce = 0) cannot be cancelled on-chain – cancellation is done off-chain by stopping cosignature issuance
• The PP and Settings Registry both emit UpdatedCollectionPaymentSettings events with DIFFERENT signatures – indexers must listen on both contracts

Related Skills

• payment-processor-creator – Configure creator payment settings, pricing, and royalties before trading
• permitc-protocol – PermitC fundamentals (approvals, signing, nonces) used for time-bound NFT listings
• apptoken-general – ERC-721C/ERC-1155C token standards and ecosystem overview