About the role We are seeking a Senior Blockchain & Backend Engineer to help maintain and evolve Debita by Neitec, our on-chain asset‐based private credit infrastructure. This role combines production smart contract engineering with backend integration work across Web3 infrastructure, payment rails, custody providers and off‐chain financial systems.
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The ideal candidate has already deployed and maintained smart contracts handling real‐world capital, understands the full lifecycle from testnet to mainnet, and is comfortable building the backend services required to connect on‐chain financial logic with APIs, databases, wallets and settlement flows.
Requirements Fluent Spanish is required, as the role involves working closely with Spanish‐speaking teams and stakeholders.
The candidate must be based in Spain, preferably in Madrid, or willing to work within the Spanish time zone.
This is NOT a junior position. We need someone who has:
Deployed and maintained smart contracts handling real‐world capital in production
Experienced the full lifecycle of blockchain projects from testnet to mainnet
Debugged critical production issues under pressure
Made architectural decisions that impact security and scalability
Key distinction You'll split your time 50/50 between:
Smart Contracts & SDK Layer (EVM, Solidity, TypeScript SDK)
API Integration Layer (Backend services consuming Web3 infrastructure)
Core responsibilities Smart contract development & maintenance (50%) Production contract management Maintain and upgrade existing bond issuance contracts
Deploy new bond instances to mainnet following strict security protocols
Monitor on‐chain operations and respond to incidents
Coordinate with auditors for security reviews before major upgrades
Financial logic implementation Implement complex amortization schedules (French, bullet, hybrid models)
Design settlement mechanisms (atomic on‐chain vs hybrid off‐chain)
Build compliance enforcement at the smart contract level (KYC/AML whitelisting)
Integrate with Chainlink Automation for scheduled operations (interest payments, redemptions)
SDK development Maintain TypeScript SDK used by API
Generate and version ABIs, TypeChain bindings, and contract interfaces
Write integration tests ensuring SDK behavior matches contract state
Document breaking changes and coordinate releases with API team
Web3 API integration (50%) Backend services Integrate SDK into NestJS API services
Build reliable transaction management (nonce handling, gas estimation, retry logic)
Design off‐chain balance registries synchronized with on‐chain state
Payment rails & custody integrations Integrate with fiat on/off ramp providers (bank accounts, payment processors)
Connect payment rails: crypto transfers, SEPA, ACH and local payment methods
Integrate with liquidity providers and custody solutions (MPC wallets, institutional custodians)
Build synchronization mechanisms between on‐chain state and off‐chain legacy systems
Coordinate atomic or hybrid DVP (Delivery vs Payment) settlements across chains and rails
Handle wallet management, signing flows, and key rotation strategies
Implement transaction batching and gas optimization at API level
Technical requirementsBlockchain / Smart Contracts Production solidity experience 2+ years writing production Solidity
Deployed contracts managing real fund(s) on mainnet
Handled production incidents (reverted transactions, gas spikes, oracle failures)
Experience with upgradeable contracts (UUPS, Transparent, or Beacon proxies)
Deep understanding of EVM internals (storage layout, gas optimization, assembly when necessary)
Concrete skills Write gas‐efficient Solidity following best practices
Debug failed transactions using Tenderly, block explorers, or local forking
Perform upgrades on live contracts without downtime or data loss
Implement custom error handling, events, and role‐based access control (OpenZeppelin)
Understand reentrancy risks, front‐running, and common attack vectors
Tools & frameworks Foundry (primary) or Hardhat (legacy support)
OpenZeppelin Contracts (v5.x upgradeable suite)
Chainlink Automation (keeper‐compatible contracts)
Backend development TypeScript/Node.js 3+ years building production Node. xiphteb js services
Experience with NestJS or similar enterprise frameworks
Proficient in ethers.js v6 (contract interactions, wallet management, event parsing)
Async/await patterns, error handling, and retry mechanisms
Database & state management PostgreSQL for off‐chain data (transactions, balances, audit logs)
Understanding of eventual consistency in blockchain‐to‐database sync
Experience with migration scripts and schema versioning
API design RESTful API design for financial operations (idempotency, validation)
WebSocket streams for real‐time blockchain events
Rate limiting and authentication for sensitive endpoints
Error handling that doesn't leak private keys or internal state
Integration & traditional finance Bridge blockchain with legacy systems Experience integrating blockchain with traditional banking/payment infrastructure
Understanding of fiat on/off ramps (convert crypto fiat via bank accounts)
Knowledge of payment rails: SEPA (Europe), ACH (US), wire transfers, local payment methods (SPEI/Mexico, Pix/Brazil, FedNow, etc.)
Bank account integration experience (APIs for deposits, withdrawals, reconciliation)
Custody provider integrations (MPC wallets, institutional custodians, key management services)
Liquidity provider coordination (ensuring sufficient funds for settlements)
On‐Chain / Off‐Chain state synchronization Design systems that maintain consistency between blockchain state and database state
Handle eventual consistency and reconciliation between on‐chain events and off‐chain records
Build idempotent operations that can safely retry without double‐spending or data corruption
Monitor and alert on synchronization drift (on‐chain balance ≠ database balance)
Delivery vs Payment (DVP) coordination Atomic DVP: On‐chain smart contract settlement (payment + delivery in single transaction)
Hybrid DVP: Coordinate on‐chain delivery with off‐chain payment (via bank transfer, custody ledger)
Handle multi‐leg settlement flows (bond issuance → fiat payment confirmation → token delivery)
Implement rollback/refund logic when one leg of DVP fails
Experience with escrow mechanisms, multi‐signature approvals, or atomic swaps
Concrete skills Integrate with payment processor APIs
Handle currency conversion and multi‐currency accounting
Design webhooks and callbacks for asynchronous payment confirmation
Understand regulatory requirements for AML/KYC in payment flows
Financial protocols understanding Capital markets basics
Bond lifecycle: issuance → coupon payments → principal redemption → maturity/default
Atomic DVP (fully on‐chain: smart contract ensures simultaneous delivery + payment)
Hybrid DVP (on‐chain delivery coordinated with off‐chain payment via bank transfer or custody ledger)
Escrow and multi‐signature approval flows
Amortization schedules
Roles management
Tokenization concepts Security token standards (ERC‐20 with compliance hooks)
On‐chain vs off‐chain compliance (hybrid models)
Custodial vs non‐custodial wallets in institutional context
Nice-to-have experience Advanced blockchain Multi‐chain deployments (experience with 2+ EVM chains in production)
MEV awareness and mitigation strategies (private mempools, Flashbots)
Gas optimization at scale (batch operations, signature aggregation)
Experience with account abstraction (ERC‐4337) or smart contract wallets
Domain experience Built or maintained aReal‐World Asset (RWA) protocol
Experience with Security Token standards (ERC‐3643, ERC‐1400)
Worked unregulated fintech (securities, payments, custody)
Integrated with institutional custody
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