Zappay

P2P Naira ↔ STRK Marketplace. Send ₦ via any Nigerian bank — receive STRK instantly on-chain.

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TL;DR

• Seller locks STRK in an on-chain escrow with their bank account number and NGN price.
• Buyer sends Naira via any Nigerian bank (Opay, PalmPay, Kuda, Moniepoint, GTBank, etc.).
• The Eigen TEE calls the Paystack API to verify the transfer and signs the receipt.
• The signed proof is submitted on-chain, validated against the escrow, and STRK is released to the buyer.

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Architecture

┌─────────────┐   deposit STRK + account no.   ┌──────────────────┐
│   Seller    │ ──────────────────────────────► │  Starknet        │
│             │                                  │  Escrow Contract │
└─────────────┘                                  └────────┬─────────┘
                                                         │
┌─────────────┐   Naira bank transfer (off-chain)        │
│   Buyer     │ ──────────────────────────►              │
│             │   Opay / PalmPay / Kuda /                │
│             │   Moniepoint / GTBank / etc.             │
└──────┬──────┘                                          │
       │  claim_funds(signature, receipt)                │
       └─────────────────────────────────────────────────┘
                              │
                              ▼
                    ┌──────────────────┐
                    │  Eigen TEE       │
                    │  - Paystack API  │
                    │  - Verifies txn  │
                    │  - Signs receipt │
                    └──────────────────┘

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Flow

1. Deposit – Seller locks STRK, sets their bank account number and price per STRK in NGN.
2. Signal Intent – Buyer signals intent to buy (1-hour lock).
3. Pay – Buyer sends Naira to seller's account via any Nigerian bank.
4. Verify & Sign – Buyer pastes the Paystack transaction reference. TEE calls Paystack API, confirms the transfer, and signs the receipt.
5. Claim – Buyer submits the signed proof on-chain; contract validates and releases STRK.

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Supported Banks

Any Nigerian bank that processes transfers through Paystack:

• Opay
• PalmPay
• Kuda
• Moniepoint
• GTBank
• Access Bank
• Zenith Bank
• First Bank
• UBA
• And all other NIBSS-connected banks

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Deployments

Sepolia (Testnet)

Resource	URL
Contract (Voyager)	0x045f0dda5b49e8c994aceeb74f08dcbd47da88cd1ab2085221e76e3f78466c45
Deploy Transaction	0x034cb779c35ce0fd2b2fe315ecd793230179cf69e262d1752720eb303b1a09bd
Class Hash	0x6ff5c9ddc6a50950771f4b0c666ef2487b9452a1f9f41e4d0a23d56cfb2f5b3
Declare Transaction	0x3355507bce26aa13bfc1e7286651c4b49933e543643743be9c0960fe0b79099

Constructor args:

• signer_public_key: 0xd84917d613a8307d167e409503d85bef759f26bbf92cd87e1c994731a104c5
• token_address (Sepolia STRK): 0x04718f5a0fc34cc1af16a1cdee98ffb20c31f5cd61d6ab07201858f4287c938d

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Repo Structure

Zappay/
├── src/           # Cairo smart contracts (Starknet)
├── eigentee/      # Eigen TEE service (Paystack API + Express)
├── frontend/      # React + StarkZap frontend
└── README.md

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Quick Start

1. Smart contracts (Cairo)

scarb build
scarb test

src/lib.cairo declares the escrow module and is required as the Scarb crate root.

2. Eigen TEE service

cd eigentee
npm install
cp .env.example .env   # Set MNEMONIC and PAYSTACK_SECRET_KEY
npm run build && npm start

Get your Paystack secret key from dashboard.paystack.com.

3. Frontend

cd frontend
npm install
cp .env.example .env   # Set VITE_ESCROW_ADDRESS, VITE_TEE_SERVER
npm run dev

Production build:

cd frontend
npm run build

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Tech Stack

• Smart contracts – Cairo on Starknet (Sepolia testnet)
• Wallet – Cartridge Controller via StarkZap SDK (starkzap)
• TEE – Eigen TEE with Paystack API for Nigerian bank transfer verification
• Frontend – React + Vite, white/orange UI theme

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Currency

Denominated in NGN (Nigerian Naira ₦). Live STRK/NGN rates fetched from CoinGecko every 60 seconds.

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Security

• TEE attestation – The Eigen TEE is attested; the signing key never leaves the enclave.
• Nullifiers – Each transaction reference can only be used once on-chain.
• Intent expiry – Buyer has 1 hour to complete payment and claim after signaling intent.

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In-App Help Bot

Zappay includes a built-in helper bot (the ? button at the bottom-right). Supported topics:

Topic	Example phrases
About the app	"what is zappay", "how does this work", "explain"
Buying STRK	"how do i buy", "buy strk", "i want to buy"
Selling STRK	"how do i sell", "sell strk", "create order"
Signal Intent	"signal intent", "what is intent", "reserve order"
TEE verification	"what is tee", "how is payment verified", "verification"
Withdrawing	"withdraw", "get my strk back", "cancel sell order"
Wallet	"connect wallet", "cartridge", "how to connect"
Cancel intent	"cancel intent", "change my mind", "undo intent"
Price / rate	"price", "rate", "naira", "strk price", "ngn"
Safety	"safe", "secure", "scam", "can i get scammed"
Testnet	"sepolia", "testnet", "test", "real money"
Faucet	"faucet", "get strk", "free strk", "test strk"
Trade history	"history", "past orders", "settled", "completed"
Transfers	"transfer", "send strk", "send to friend"

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License

MIT