pay-chat

AI assistant inside MiniPay that reads Celo on-chain data, paid per query in USDT. Every answer costs $0.02 USDT, settles on Celo Mainnet via x402, and emits a verifiable on-chain receipt.

🌐 Live: https://pay-chat-nine.vercel.app 📜 PromptReceipt contract (verified): 0x962BC4ad7671Db17d975AB42D4dA5110bC13b66a

What makes it different from a generic chatbot

• Reads the chain. Paste any Celo tx hash and get a plain-language explanation. Drop a contract address and get its name, owner, age, power functions (mint / pause / upgrade / transferOwnership), and recent activity. Ask "what have I been doing on Celo?" and get a summary of your actual transactions. None of this is invented — it's fetched live from Celo RPC + the Etherscan V2 unified API and injected as authoritative context before the model answers.
• Tap-to-copy chips. Addresses and tx hashes in answers are rendered as compact chips that copy the full hex on click and link to Celoscan in one tap.
• Smart-wallet aware. Detects EIP-7702 delegated EOAs (account abstraction) by bytecode prefix and routes them through the activity path instead of asking for source code that doesn't exist.
• Pay per query, not per month. No subscription, no signup, no credit card. Sign one EIP-2612 permit per question — the user never pays gas.
• Receipts on-chain. Every answer emits a PromptPaid(user, model, queryHash, timestamp) event from a verified Ownable contract — auditable, expensable, no trust in the backend required.

How it works

1. User asks a question inside MiniPay (or any browser via the explicit Connect button).
2. Backend returns HTTP 402 Payment Required per the x402 protocol.
3. User signs an EIP-2612 permit for $0.02 USDT — no on-chain transaction for the user, no gas.
4. Server-side thirdweb facilitator settles the payment on Celo and exposes the payer address.
5. Chain-context enrichment (defensive, wrapped in try/catch so it can never break the flow):
   • Regex scans the user's message + the assistant's previous reply for 0x[a-f0-9]{64} (tx hashes) and 0x[a-f0-9]{40} (addresses).
   • Heuristic intent detector matches phrases like "my last transactions" / "mi historial" to also enrich with the connected wallet's activity.
   • For each match, viem fetches the tx receipt (decoding ERC-20 Transfer events) or classifies the address (EOA / contract / EIP-7702 smart wallet) and pulls the right structured summary from Etherscan V2 (chainid=42220).
   • The structured blocks are injected as a role: "system" message before the model is called, with temperature: 0.3 to keep it grounded.
6. LLM call: Groq Llama 3.3 70B, with Cerebras gpt-oss-120b as automatic failover. A preflight ping ensures the user is never charged when both providers are unreachable.
7. PromptReceipt.logPrompt(...) is enqueued from the server wallet so the on-chain receipt event lands a few seconds later.

Stack

• Framework: Next.js 16 (App Router · Turbopack) · TypeScript strict
• Styling: Tailwind v4 · @tabler/icons-react
• Wallet: wagmi 3 + viem 2 + injected() connector
• Payments: thirdweb x402 (useFetchWithPayment client side, settlePayment + facilitator server side)
• Chain reads: viem public client + Etherscan V2 unified API (single key covers all Etherscan-family explorers, including Celoscan)
• LLM: Groq Llama 3.3 70B with Cerebras gpt-oss-120b as automatic failover
• Contracts: Hardhat 2 + Solidity 0.8.28 + OpenZeppelin Ownable
• Deploy: Vercel with GitHub auto-deploy on main
• Package manager: pnpm

Local development

pnpm install
cp .env.example .env.local   # fill in the secrets
pnpm dev                     # http://localhost:3000

You'll need keys for: Groq, Cerebras, thirdweb (client + secret), the thirdweb-managed server wallet address, and an Etherscan V2 API key (the same key works on Celoscan).

To test inside MiniPay's Developer Mode, load the production URL directly (no tunnel needed) or expose localhost:3000 over HTTPS with ngrok http 3000 and paste the tunnel URL into the Mini App test page.

Scripts

Script	What it does
pnpm dev	Next.js dev server (Turbopack)
pnpm build	Production build
pnpm lint · pnpm typecheck	ESLint · tsc --noEmit
pnpm test	Vitest unit tests (chain-context + Etherscan wrapper + message tokenizer)
pnpm hh:test	Hardhat contract tests
pnpm hh:deploy:celo	Deploy PromptReceipt.sol to Celo mainnet
pnpm build:icons	Rasterize public/icon.svg into PNG icons

Project layout

app/                          Next.js App Router (chat UI, /api/chat, /tos, /privacy)
components/
  ChatApp.tsx                 Mobile-first chat UI with new-chat reset, sample prompts
  MessageContent.tsx          Renders addresses + tx hashes as tap-to-copy chips
  Footer.tsx, WalletBadge.tsx
hooks/                        useAutoConnect, useIsMiniPay, useIsMounted
lib/
  wagmi.ts                    wagmi config (Celo + Celo Sepolia, injected connector)
  x402-server.ts              thirdweb client + x402 facilitator + payment token config
  payments.ts                 client-side wrapFetchWithPayment helper
  llm.ts                      Groq + Cerebras router, system prompt, chain-context injection
  prompt-receipt.ts           Fire-and-forget logPrompt() via thirdweb Engine
  celo-public.ts              viem public client for server-side chain reads
  etherscan.ts                Etherscan V2 wrapper (concurrency-limited + retried)
  chain-context.ts            Reference detector + tx / address / self-history enrichment
  parse-message.ts            Tokenizer for chip rendering
  site.ts                     Shared product constants (URLs, contract address, known tokens)
contracts/                    PromptReceipt.sol (Ownable, emits PromptPaid)
scripts/                      deploy-prompt-receipt.ts, build-icon.mjs

License

MIT

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Built for Celo Proof of Ship. Support: https://t.me/paychat_support.