"Hello Everyone! & gm"


Everyone knows blockchain UX(User Experience) could be improved. My brother had accidentally sent a month's salary of USDC to the wrong exchange address, he wished it was easier getting back his funds. He mentioned if there was a Paypal/Interact-like interface where he could withdraw his funds.

What it does

Paylock charges 0.5% per transaction (capped at 50USD) determined on chain to allow users to create (Withdrawable) ERC20 payments and provides the ability to withdraw/redeem payments without paying gas. Users optionally could notify payment receiver user via text-message

How I built it

Front-end: React/Next.js frameworks and Tailwindcss. Deployed on Vercel.

Back-end/Contract: Remix-IDE to develop and test Contracts. OpenZeppelin Defender Relayer to support gas-less payments. ChainLink Price Feed Oracles to determine fees per transaction.

Contract Addresses

Mumbai MinimalForwarder, PaylockAddress

Goerli MinimalForwarder , PaylockAddress

Challenges I ran into

  • I had a tough time integrating OpenZeppelin Defender to relay transactions. I was able to integrate gasless functionality to support redeeming and withdrawing payments without paying gas fees.
  • Determining maximum fees per transaction (0.5%) by calculating the USD value of the transaction and capping fees at 50USD in the contract.
  • Creating a V1 in a relatively short period of time!

Accomplishments that I'm proud of

  • I implemented gasless functionality for withdrawing issued payments.
  • I was able to build this platform during the period of the hackathon by myself.

What I learned

  • I learned alot about integrating Chainlink price feeds/OpenZeppelin Defender Relayer in my contracts.
  • There is no floating point in Solidity. Ethereum addresses have 64 character hex string.
  • I learned that TRON is very similar to EVM networks( i.e same contract code but deployment and interactions with contract is different)

What's next for PayLock


  • Payments table sorting + timestamps
  • Add tooltips


  • Multi-Payments
  • End-to-end gasless interactions
  • Add Contacts (Addresses Book) and Avatars
  • Cross-Chain Transfers to support Tron (TRC20 transfers ) network

Built With

  • chainlinkpricefeeds
  • hardhat
  • nextjs
  • openzeppelindefender
  • react
  • solidity
  • tailwindcss
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