Contact person: Business Client

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Location: Frisco, United States

Budget: Recommended by industry experts

Time to start: As soon as possible

Project description:
"The application must implement an in-app crypto payment layer supporting both on-chain (Bitcoin, USDT) and off-chain (fiat/local currency which I will specify in chat) transactions with seamless interoperability. Users should be able to initiate and receive payments via QR or NFC, with all transaction metadata (amount, wallet address, currency type) embedded in the QR payload to eliminate manual entry.

The wallet system should be multi-currency, initially supporting Bitcoin and USDT, and capable of generating unique deposit addresses (per user or per transaction). It must handle wallet creation, signing, and broadcasting transactions securely — either through a custodial backend (managed private keys) or non-custodial approach (client-side key generation). I am open to both.

I have a chatting module implemented in my mobile which the payment interface will integrate with the wallet service to trigger P2P transfers directly from the user’s balance, while merchant endpoints should support both QR-based and NFC tap-to-pay payment flows. The backend must handle merchant transaction routing, instant confirmations, and settlement conversions between crypto and the local currency.

Finally, the system should support virtual Visa card issuance via integration with a third-party card API (e.g., Striga, Mercuryo, or Transak), linked directly to users’ crypto balances for fiat spending.

Note: If you are able to do a subset of the task then still consider applying, I'd be willing to hire if you can do quality work." (client-provided description)