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CrypTap – Non-Custodial Crypto Payment Platform

The project I'm proudest of: a complete non-custodial crypto payment platform built end-to-end — smart contracts on 7 EVM chains and Solana, an in-store POS with a BLE hardware signing device and ESP32 firmware, a hosted e-commerce checkout with trustless permissionless settlement, WooCommerce/Shopify plugins, and merchant/owner/admin dashboards. CrypTap never holds, signs for, or transmits merchant funds — and I built every layer of it.

Toni Dumancic — Architect & Full-Stack Developer (contracts, firmware, frontend, backend)
CrypTap – Non-Custodial Crypto Payment Platform

Overview

CrypTap is a full crypto payment platform for real businesses — cafés, shops and online stores that want to accept crypto without handing their money to a middleman. Most "accept crypto" providers are effectively crypto banks: they receive funds in their own name, custody them, and pay the merchant out later. CrypTap is built on the opposite principle, and the entire architecture defends one invariant:

CrypTap never holds, signs for, or transmits merchant funds. Everything that touches money happens client-side and on-chain; the backend only tracks payment intents and verifies their status.

There is no part of this platform I didn't build: the EVM contracts, the Solana program, the POS, the payment page, the hardware device integration and firmware, the e-commerce product with its settlement contracts and keeper, the store plugins and SDK, the dashboards, the admin panel and the backend.

On-chain foundation

EVM — 7 chains

Deployed on Polygon, Ethereum, BSC, Arbitrum, Optimism, Avalanche and Base. Instead of deploying a full contract per payment, an InvoiceV2 factory creates minimal-proxy clones (~200k gas per invoice, a fraction of a full deploy). Addresses are CREATE2-predicted from the payment parameters — the pay-to address exists before anything is on chain, so the customer can be shown a QR code instantly. Settlement is restricted onlyMerchantOrDeployer, native coins and ERC-20 (USDC/USDT/DAI…) both supported.

Solana

A native Anchor (Rust) program — one PDA per invoice, supporting SOL and SPL tokens, with the same intent-tracking flow as EVM. Not a bridge or a wrapper: a first-class second contract stack.

In-store: POS + hardware

  • Merchant POS — a fully client-side web app. It creates the invoice on-chain, shows live payment status, and handles tips, tax and fiat conversion with real-time rates. Settling, cancelling and refunding all happen from the browser with the merchant's own key.
  • CrypTap device — a BLE hardware terminal (ESP32, custom firmware) that pairs with the POS and signs every transaction on-device. The private key never touches the browser, the network, or CrypTap. This is the difference between a demo and something a business can actually run.
  • Customer payment page — QR code with countdown, wallet deep links, live on-chain confirmation, and export/send-remotely options. Includes recovery flows for edge cases (funds received but not yet distributed) so no payment is ever stranded.

E-commerce: trustless settlement with zero merchant infrastructure

Online stores break the POS assumptions — nobody is at the counter holding a key when a shopper pays at 3 AM. CrypTap Commerce solves it without ever taking custody:

  • CommerceSettler contract (one per chain) — every commerce invoice address is derived deterministically: intentIdHash = keccak256(merchant, developer, token, amount, feeBps, nonce), and the factory predicts the clone address from it. A keeper that submits wrong parameters computes a different address that holds no funds — so settlement needs no signatures, no attestations, no trust.
  • On-chain gas tank — merchants pre-fund gas for their own settlements from the dashboard, keyed to their payout address; only they can withdraw. The keeper is reimbursed on-chain, only when a settle actually distributed funds (anti-grief), capped by the merchant's max gas price.
  • Keeper — a settle bot that finds funded checkouts and triggers settlement on EVM and Solana. It holds no merchant keys and custodies nothing; its telemetry is exposed in the owner dashboard.
  • Hosted checkout + REST API — machine-to-machine API keys, idempotent checkout creation, and HMAC-signed outbound webhooks so a store backend knows the moment a payment lands.
  • Integrations — WooCommerce and Shopify plugins, plus a commerce-js SDK for custom storefronts.

Operations layer

  • Owner dashboard — revenue analytics, device management, payout wallets, transaction history, sweeps, fee tiers and keeper telemetry.
  • Admin panel — merchants, users, transactions, logs and commerce oversight.
  • Backend — Flask + SQLAlchemy. It receives intents, stores them, and independently verifies their status on-chain with a checker and scheduler. It can see everything and touch nothing — by design it has no keys and no custody.

Security model in one breath

Client-side signing everywhere; hardware key isolation on the BLE device; deterministic address binding instead of signed attestations; permissionless settlement that punishes wrong inputs economically instead of cryptographically; a backend that is a read-only observer of the chain.

Tech Stack

  • Solidity (Foundry) — factory + minimal-proxy invoice contracts, CommerceSettler, on 7 EVM chains
  • Anchor / Rust — Solana invoice program (PDAs, SOL + SPL)
  • Next.js + TypeScript — POS, payment page, hosted checkout, owner dashboard, admin panel
  • Flask + SQLAlchemy — intent tracking backend, on-chain checker, keeper
  • ESP32 / BLE — hardware signing terminal firmware
  • ethers.js / @solana/web3.js — all chain interaction, in the browser

Cryptography, hardware, smart contracts, plugins and plain old web engineering — one person, one coherent platform. This is the project I point to when someone asks what I can build.