PayLink Kit — non-custodial multi-chain stablecoin checkout

The complete source for a payment-link service that takes USDT and USDC on six EVM chains. Buyers pay from whatever chain they already hold; the money goes straight to your wallet. No signup, no KYC, no custody, no platform fee.

Six chains, two stablecoins — BSC, Ethereum, Polygon, Arbitrum, Base, Optimism. 11 payment rails from one wallet address.
The amount is the identity. Each invoice gets a unique micro-amount, so a transfer on any chain matches the right order. No per-chain order numbering, no collisions.
Zero dependencies. Plain Node. No database, no ORM, no build step. Two files and a folder of HTML.
You are not a custodian. The code reads public Transfer events. It never signs, never holds a key, never touches the money.
Multi-seller by design — each payout address gets its own chain cursors, so one instance can serve many wallets without cross-matching.

49 USDT

Pay in USDT or USDC — BSC, Ethereum, Polygon, Arbitrum, Base or Optimism. The download link unlocks the moment the transfer confirms — no account needed.

Buy — 49 USDT

Try it before you buy

The live service is running right now — paste any EVM address, get a real payment link. No signup.
Create an invoice, open it, and watch the chain picker. That is the whole product.
The kit is the same code, plus the parts you need to run it yourself.

What is in the package

paybridge.js — the chain watcher: six chains, per-address cursors, decimals read on-chain, BigInt amount math
paylink-server.js — invoice API, seller dashboard, buyer checkout, static server
web/index.html + web/pay.html — the two pages, no framework
paylink-test.js — 16 assertions covering multi-seller isolation, cursor independence, amount-pool saturation, address validation
README.md — deploy notes, the six measured RPC quirks, and the failure modes worth knowing

The numbers that matter (measured, not claimed)

chain	blocks per getLogs call	round trip	note
BSC	1000	375 ms	18 decimals on USDT/USDC
Ethereum	10000	578 ms	6 decimals
Base	3000	369 ms	USDC only — no official USDT
Polygon	5000	~540 ms	6 decimals
Optimism	5000	~522 ms	6 decimals
Arbitrum	3000	~530 ms	publicnode returns 403 on eth_getLogs — must use arb1.arbitrum.io

Every row above was measured from a real machine, not copied from docs. The Arbitrum row alone saves an afternoon.

Run it

# no install step — plain node
node paylink-server.js

# it prints:
#   PayLink on http://127.0.0.1:8901
#   rails: 11 channels across 6 chains

# create an invoice
curl -s localhost:8901/api/invoice -H 'content-type: application/json' \
  -d '{"payTo":"0xYourWallet","price":49,"title":"Invoice #1"}'

Put it behind any reverse proxy. If you already run a Cloudflare tunnel, add a path rule — the kit ships the exact ingress snippet.

The failure modes it already handles

Exchange withdrawal fees. A buyer paying 19.27 from Binance may land 18.27. Exact matching alone would lose that sale — tolerance matching catches it, and the order is flagged underpaid.
RPC failure must not advance the cursor. If a block range fails, the cursor stays put and the range is retried. Slow is fine; silent loss is not.
Amount-pool saturation. Only 98 cent-values exist per price. Past that, invoices collide and two buyers fight over one transfer. The pool tiers up to 998 and then refuses to issue rather than hand out a doomed invoice.
Unmatched deposits are logged, never swallowed. Someone sends the wrong amount and it does not vanish — it lands in unmatched-deposits.log with the txid.
Decimals are read from the contract, not hardcoded. BSC is 18, everyone else is mostly 6, and getting this wrong is a 10¹² error.

What this does not do

It does not convert between tokens — 1 USDC counts as 1 USDT, which is fine for stablecoin checkout and wrong for anything else.
It does not handle BTC, Tron, or Solana. EVM only. Adding Tron is a separate watcher (the original store had one).
It is not a hosted service — you run it. That is the point: nobody can freeze your checkout.
It is not audited. Read the code; it is under 1500 lines total.