Sendpay

Inspiration

Accessing crypto in Africa on Starknet is still inconvenient for everyday people. Many users rely on multiple apps just to buy, send, convert, or use digital assets for basic bills. Banks offer fiat tools but not crypto flexibility, and most crypto apps don’t support seamless real-world utility. Sendpay was inspired by the need for a single wallet that lets Africans move between crypto and fiat seamlessly on Starknet—pay bills, buy airtime, cash out, and transact without friction.

What it does

Sendpay is a crypto wallet with fiat superpowers built for Africa. It supports:

• Crypto and fiat wallet system
• On-ramp and off-ramp (e.g., USDC to Naira)
• Crypto transfers
• Bank verification and user onboarding
• Airtime, data subscriptions, and bill payments

How we built it

Sendpay is powered by a mix of blockchain, web, and financial tooling:

• Smart contracts → Cairo (deployed on Starknet mainnet & Sepolia)
• Backend → Express.js, TypeScript, Apibara for indexing, MongoDB
• Frontend → Next.js, JavaScript/TypeScript, TailwindCSS
• Wallet infrastructure → Chipi-stack
• Payments → Flutterwave integration
• Off-chain signatures → Custom signing + onchain verification We designed user onboarding with bank verification and created flows that merge crypto transfers with real-world payments.

Challenges I ran into

I faced several technical and infrastructure hurdles:

• Architecture design — Planning the full flow from smart contracts to APIs to wallets
• Indexer deployment — Free hosting services kept shutting down, so I implemented uptime monitoring to ping and keep the indexer alive
• Flutterwave integration — IP whitelisting and gateway configuration was a headache
• Signature service — Building a secure off-chain transaction signing + onchain verification system required strong security design

Accomplishments that I am proud of

• Working product demo already live
• Smart contracts deployed on both StarkNet mainnet and Sepolia
• Smooth onboarding with KYC/bank verification
• Clean and simple wallet experience with USDC offramp to naira
• Functional architecture across crypto and fiat services

What I learned

I gained experience in:

• Designing secure blockchain-to-backend architecture
• Managing off-chain signing systems safely
• Deploying and maintaining indexers in restricted environments
• Combining traditional payment gateways with smart contract flows
• Developing user-centric onboarding for mixed crypto/fiat ecosystems

What's next for Sendpay

We’re expanding the platform with:

• Early user onboarding and pilot testing
• Full integration of bill payments and subscriptions
• Deeper mobile support and app development
• Scaling on/off-ramp services across more African regions
• Iterating the user experience and growing real usage

Built With

• apibara
• cairo
• express-js
• express.js
• flutterwave
• javascript
• mongodb
• nextjs
• tailwindcss
• typescript