Freelance Senior .NET developer with Payments Experience

Behalf of our client, we are looking for Freelance Senior .NET developer with Payments Experience.

Project/Client: fintech

Location: Lithuania

Start date: ASAP

Duration: 12 months

Seniority: senior

Role Overview:

We are seeking an experienced .NET Developer to join a fintech engineering team. The position requires deep knowledge of banking standards (ISO 20022), real-time payment solutions, and strong .NET expertise. Knowledge of UK payment regulations is highly preferred.

Key Requirements:

• 6+ years of experience with C# and .NET (Core/6/7/8)
• Advanced knowledge of ISO 20022 and SEPA payment formats
• Hands-on experience with SWIFT, FPS, BACS, CHAPS, TARGET2
• Familiarity with APIs for PayPal and Banking Circle
• Proficient with REST, SOAP, SFTP, XML/JSON
• Secure coding expertise, SQL Server, message queues, Docker
• Excellent communication skills in English
• Experience with UK payment regulations is highly preferred
• Experience with Open Banking is a must

Nice to Have:

• Background in core banking systems or digital wallets
• Experience with cut-off times, clearing, and settlement processes

Responsibilities:

• Develop and maintain backend payment processing services using .NET Core (C#)
• Process ISO 20022 (pain.001, camt.053) and SWIFT MT/MX payments
• Integrate with various bank APIs and file-based communication channels
• Oversee the full lifecycle of payments—from initiation to reconciliation
• Ensure compliance, robust error handling, and auditing
• Collaborate with cross-functional teams to deliver secure, scalable platforms
• Maintain technical documentation and implement new payment integrations
• Participate in code reviews, testing, and CI/CD pipelines