crypto coin transaction helper needed

Budget: $30 - $250

I want customers to be able to pay me in Bitcoin, Ethereum and Litecoin no matter which of my touchpoints they are on—web, mobile or a small desktop app. Your job is to wire up end-to-end payment processing: create or connect the wallets, generate addresses on demand, listen for confirmations and send clear callbacks to my backend so that orders can be fulfilled instantly and securely.

Here is how I picture the flow. A shopper chooses one of the three coins, the system produces a unique address or QR code, the payment is detected, and my server is notified with the amount and at least one confirmation. From there I take over. Speed, security and clean logging are non-negotiable.

Deliverables • A lightweight service or API that covers address generation, confirmation tracking and error handling for BTC, ETH and LTC • Integration snippets or SDK examples for JavaScript (web), Kotlin/Swift (mobile) and either Electron or.NET (desktop) showing how to call that service • Clear setup docs plus a short test script so I can run end-to-end test-net transactions before going live

Acceptance criteria • Successful test-net payments for all three coins on each platform, with callbacks firing exactly once per order • Code is handed over well-commented and ready for me to deploy on my own servers

If you have an existing library or gateway in mind, mention it; otherwise I am open to whatever stack you trust, provided it is stable and doesn’t lock me into high fees.