Just Pay

Just Pay is a chain-abstracted USDC payment app that turns complex multi-chain interactions into a one-tap experience. Users see one USDC balance and send payments without ever thinking about what chain they’re on. From the user’s perspective, USDC is chainless.

Under the hood, Just Pay leverages Circle’s Cross-Chain Transfer Protocol V2 (CCTP V2) to move native USDC across chains using a secure burn-and-mint model backed by a global overcollateralization pool.

One of Just Pay’s core innovations is its single-signature architecture: users authorize just one transaction, and the app handles all multi-chain coordination behind the scenes. No wallet pop-ups, no chain switching, no re-approvals.

Key strengths:

• Chainless USDC Experience: Users interact with a unified USDC balance, no matter which chain their funds are on.
• Single-Signature Simplicity: Complex cross-chain transfers and aggregation logic are triggered with just one user signature.
• Fast, Secure Transfers: Transactions complete in seconds—even on slow-finality chains like Ethereum L1—via CCTP V2’s Fast Transfer mechanism.
• No Bridges or Wrapping: Just Pay uses native USDC only, avoiding common bridge-related risks.

Just Pay abstracts away blockchain complexity entirely—bringing the security of native USDC and the performance of modern fintech into one unified experience.

We built Just Pay as a full-stack dApp to enable single-signature, chainless USDC transfers using @Circle’s CCTP V2.

The frontend is built with Next.js, integrating RainbowKit and wagmi for wallet connectivity and signature handling. Our backend uses Node.js and MongoDB to manage session state and transfer coordination. Smart contracts are written in Solidity and developed with Hardhat.

Just Pay leverages CCTP V2’s Fast Transfer and Iris API to perform near-instant native USDC transfers without bridges or wrapped tokens. We abstract away chain logic entirely—users see one balance, and everything else is handled under the hood.

A particularly hacky and critical component is our custom signature mechanism. We designed a scheme that lets the user sign once for multi-chain operations, while embedding intent, function scope, expiration, and allowed chains into the payload. Each contract validates this context to prevent misuse or replay, enabling secure, cross-chain execution with a single signature.

Using CCTP V2 gave us the speed, security, and composability needed to create a chainless payment experience that feels like modern fintech.