I will build custom rest apis and integrate billing apis

G
guillesotoblanc
G
guillesotoblanc
Guillermo S
build custom rest apis and integrate billing apis
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build custom rest apis and integrate billing apis
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build custom rest apis and integrate billing apisbuild custom rest apis and integrate billing apisbuild custom rest apis and integrate billing apisbuild custom rest apis and integrate billing apis

About this gig

Looking for a Senior Backend Developer to build reliable APIs or integrate third-party billing and payment systems?


I am a Computer Engineer with 5+ years of experience in banking, fintech, and SaaS platforms. I specialize in building high-performance REST APIs and integrating payment gateways, automated invoicing, and tax APIs.


Services Provided:

  • Custom REST APIs: Built with C# .NET Core, Python Flask, or Node.js.
  • Billing & Payments: Stripe, PayPal, recurring billing, Tax/VAT APIs, and XML/PDF invoice generation.
  • API Integrations: Webhooks, CRM tools, external SaaS, and database synchronization.
  • Database Backend: Optimized models using PostgreSQL, SQL Server, or Oracle PL/SQL.


Featured Experience:

  • Billing & Management SaaS: Engineered a platform handling automated customer billing, tax API integration, payment status tracking, and XML payloads.


Why Work With Me?

  • Enterprise Security: Clean Architecture, token auth, and encrypted payloads.
  • Production-Ready: Includes Swagger/OpenAPI or Postman docs.
  • On-Time Delivery: Clear communication and clean code.


Please send a message before ordering to discuss your API requirements!

  • Expertise

    • Algorithms & Data structures
    • Debugging
    • Performance
    • Security
    • Design

  • Programming language

    • C#

  • Frontend framework

    • Angular
    • Bootstrap
    • Next.js
    • React.js
    • Tailwind CSS

  • Backend framework

    • Express.js
    • Flask
    • Next.js
    • Supabase
    • Other

Get to know Guillermo S

Guillermo S

Senior Full Stack Developer and Database Specialist

  • FromCosta Rica
  • Member sinceFeb 2025
  • Avg. response time1 hour

  • Languages

    English, Spanish
Hi! I’m Guillermo, a Senior Computer Engineer with 5+ years of experience architecting high-performance enterprise software, scalable REST APIs, and mission-critical databases for the banking and SaaS sectors. Whether you need a robust backend infrastructure, complex PL/SQL optimization, or full-stack web application development, I build clean, secure, and maintainable systems tailored to your business needs.

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