Blockchain & Smart Contract Engineer

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.

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:

1. Smart Contracts & SDK Layer (EVM, Solidity, TypeScript SDK)
2. API Integration Layer (Backend services consuming Web3 infrastructure)

Core responsibilities

1. 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

2. 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 requirements

Blockchain / Smart Contracts

Production solidity experience

• 2+ years writing production Solidity
• Deployed contracts managing real fundson 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.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 withSecurity Token standards (ERC-3643, ERC-1400)
• Worked unregulated fintech (securities, payments, custody)
• Integrated with institutional custody