C# SQL API & XML Export

@AwaisChaudhry

Hello, I will deliver a clean, async C# solution that talks to external accounting services via a REST API using only GET, POST and PUT, with HttpClient, typed requests, and small, easy-to-extend helpers for future endpoints. The data layer will use your SQL Server views to push and pull records to providers such as InFakt and Betterfly, with clear error handling and robust retry/backoff where needed. For the export feature, selecting Faktury in the UI will trigger an exporter that collects the relevant rows and writes FA(3) KSeF–compliant XML, validated against the official XSD so uploads to KSeF are problem-free. Deliverables include the C# API integration layer (GET/POST/PUT), the XML exporter, and a sample configuration with a schema validation proof. The code will be well commented and structured to make adding new endpoints straightforward, and I’ll provide a minimal test harness to show the end-to-end flow. Which authentication scheme and provider endpoints should we prioritize first (InFakt vs Betterfly), and are there any specific SLA or rate limits we should plan for during initial integration? Best regards,

@talhaamin

I am an expert in c#, sql and also in xml i can create rest api and also in xml generation i can create apis for your need with proper authentication and will also generate xml for the invoice

@ludiac

Hello there. I can deliver this cleanly and correctly. I have solid experience with .NET (C#), SQL Server, HttpClient-based integrations, and strict XML/XSD serialization. I will build a tidy, async REST integration layer using GET/POST/PUT only, with clear authentication handling, structured error responses, and extensible helper classes for future providers like InFakt or Betterfly. For invoices, I’ll implement a FA(3) KSeF–compliant XML exporter, generated from your SQL views and validated against the official XSD (with proof included). Code will be well-commented, testable, and PR-ready. I can start immediately and deliver within 5–7 days. Links of my similar projects. https://www.freelancer.com/projects/javascript/Car-kilometres-registration-system/reviews https://www.freelancer.com/projects/javascript/Cash-invoice-register-system/reviews https://www.freelancer.com/projects/c-sharp-programming/WPF-XAML-local-client-Live/reviews https://www.freelancer.com Thanks.

@Herculesz

Hi This is right in my lane: a clean .NET data layer that talks to external accounting APIs and an exporter that produces FA(3) KSeF XML that actually validates, not “almost works.” The most common real-world problem here is brittle integration code—sync-over-async calls, messy auth handling, and inconsistent error mapping that makes every new endpoint painful. I’ll build a tidy HttpClient-based integration layer with async GET/POST/PUT, typed request/response models, a small auth handler, and a consistent error/result pattern so adding new providers (InFakt, Betterfly, etc.) stays predictable. On the export side, the usual failure is XML that looks correct but fails XSD validation because of namespaces, ordering, required nodes, or formatting rules. I’ll generate the FA(3) structure with explicit namespaces and strongly-typed serialization (or controlled XmlWriter where needed), then validate against the official XSD as part of a repeatable proof step. SQL Server views are perfect as a stable contract: I’ll map them to invoice DTOs cleanly, keep business rules isolated, and avoid leaking SQL concerns into the XML layer. You’ll get well-commented C# code, sample config, and validation output you can run locally or in CI to prove the XML is upload-ready. Thanks, Hercules

@ZohaibRoy

⭐⭐⭐⭐⭐ Create a REST API and Invoice Exports for Your Accounting System ❇️ Hi My Friend, I hope you're doing well. I reviewed your project requirements and see you're looking for a .NET developer to create a REST API and invoice exports. You don't need to look any further; Zohaib is here to help you! My team has successfully completed 50+ similar projects focused on API integration and XML generation. I will build a clean, efficient data layer to communicate with external services and ensure your invoices are properly formatted. ➡️ Why Me? I can easily do your API integration and XML export job as I have 5 years of experience in .NET development, SQL Server, RESTful services, and XML serialization. My expertise includes creating secure HTTP requests, error handling, and structured data outputs. I also have a strong grip on database management and asynchronous programming, which will ensure your project runs smoothly. ➡️ Let's have a quick chat to discuss your project details. I can provide samples of my previous work, showcasing my skills in API development and invoice processing. Looking forward to our chat! ➡️ Skills & Experience: ✅ .NET Development ✅ REST API Integration ✅ SQL Server ✅ XML Serialization ✅ Asynchronous Programming ✅ Error Handling ✅ C# Programming ✅ Data Export ✅ Configuration Management ✅ Database Design ✅ API Documentation ✅ Troubleshooting Waiting for your response! Best Regards, Zohaib

@deepthi2889

Hi, I am a Full stack developer in Microsoft technologies. I have vast experience on working on projects that suits your requirement exactly. You can check the reviews in my profile regarding the same. My area of expertise is web application development (Web API, ASP.Net web- forms, MVC, classic ASP), Web Development ( Blazor, Angular) , web services (SOAP & RESTFul), MySql & Sql Server as back end (through stored procedures). I have 10 years of experience as a full time software developer. Kindly contact me, lets discuss your requirements.

@offshore9006

Hi there, We are a small, senior .NET team (2–3 developers) with strong experience in SQL Server, modern .NET (HttpClient, async/await), REST API integrations, and XML/XSD-driven exports for accounting and government systems. Understanding of the mission Build a clean data integration layer issuing authenticated GET / POST / PUT requests to external accounting services (e.g. InFakt, Betterfly) Use async HttpClient, typed helpers, centralized error handling, and extensible endpoint design Generate FA(3) KSeF-compliant XML invoices directly from SQL Server views Ensure full XSD validation for direct KSeF submission without manual fixes Proposed delivery API Integration Layer REST client abstraction, auth handling, retry & error mapping Extensible service providers (InFakt / Betterfly ready) FA(3) KSeF XML Exporter Strongly typed XML serialization Namespace & schema-accurate FA(3) structure Automated XSD validation proof Configuration & Validation Sample appsettings Validation test output Clean documentation Total estimate - 5-7 Days What you get Tidy, well-commented C# source Clear separation of concerns (data, API, export) Ready-to-extend architecture Pull request aligned with professional .NET standards We are comfortable working directly from SQL views, respecting existing schemas, and delivering production-ready code with no unnecessary abstractions. Happy to start and adapt to your repository and review process. Best,

@devbaloni1983

Hello, I am a .NET Developer with 15+ years of experience, specializing in building secure, scalable, and high-performance web and desktop applications. I work with C#, ASP.NET, MVC, Web API, and SQL Server to deliver robust business solutions tailored to client needs. My expertise includes custom application development, enterprise solutions, API integration, and performance optimization. Recently, I also worked on OpenAI API integration for auto-generated content, images, and social sharing, showing my ability to adopt the latest technologies. If you are looking for a dedicated .NET expert who provides quality, innovation, and timely delivery, I’d be happy to collaborate on your project.

@mobimubasir

Hello. I read your requirement i will do that. Please come on chat we will discuss more about this. I will waiting your reply

@mandavcon

Hi With my extensive skill set in .NET, C# Programming, and SQL, I am confident that I can craft a robust and reliable solution for your project. Having worked with modern .NET approaches, including HttpClient, for over a decade, clean and efficient REST-style API development is second nature to me. I am well-versed in all necessary HTTP methods (GET, POST, PUT) and can easily sync up your database with external providers such as InFakt and Betterfly. Additionally, my experience with SQL Server and clear understanding of how authentication should be implemented in API calls will ensure clean and asynchronous integration between your data layer and accounting services. Error handling is an important aspect of any software system; I'll provide a concise yet comprehensive solution that makes future endpoint additions a breeze. To further amplify the strength of my bid, HTML, CSS, JavaScript and XML have been integral parts of my journey as a professional developer which makes me your one-stop-shop for your needs. My commitment to up-to-date knowledge and passion for delivering high-quality solutions has repeatedly pleased employers I've worked with - something I would strongly look forward to replicating for you. Reagrds Mahesh

@aktarujjamana7

I’ll deliver a C# REST integration (GET/POST/PUT via async HttpClient), robust error handling, modular helpers, and a KSeF FA(3) XML exporter validating against XSD—wired to SQL views, with configuration and proof samples.

@DigitaSyndicate

⚠️You are not looking for a coder. You are looking for someone who can build this properly. That is exactly why your project stood out.⚠️ Your focus on building a robust data layer that interfaces through authenticated REST-style calls using modern .NET techniques, coupled with precise FA(3) KSeF-compliant XML invoice exports, reveals a clear commitment to reliable, future-proof automation. At DigitaSyndicate, a UK-based digital systems agency, we build precision-engineered automation, modern web platforms, and AI-driven systems designed for performance and long-term scalability. Our approach embraces asynchronous HttpClient usage, rigorous error handling, and strict schema validation to ensure secure and streamlined integration that scales seamlessly. We recently delivered a similar .NET integration syncing SQL Server sources with external APIs and producing validated XML exports. Can you share your main priorities and timeline so I can map out the right execution plan for you? Casper M. Project Lead | DigitaSyndicate Precision-Built Digital Systems.

@SamirBanna

Hello, I’m a Senior Software Engineer with extensive experience in Python automation and web scraping & C# WindowFormApp and WFP. I’ve carefully reviewed your requirements and I can deliver a reliable, production-ready solution — not a quick workaround. ✅ Clean and maintainable code ✅ Clear communication ✅ On-time delivery I’d be happy to discuss your project details and propose the best technical approach. Best regards, Samir

@wasifmuneer

Hi there, I'd love the opportunity to connect and discuss your project in detail—feel free to reach out via chat anytime. I'm a full-stack developer with strong experience in building both web and desktop applications. I’m confident I can manage and deliver your project efficiently and on time. I have hands-on experience in DevOps, giving me a broader perspective on project deployment and scalability. With the help of AI tools, and supervision of full stack developer helps this project completion asap. My technical expertise includes: MERN / MEAN Stack: Extensive hands-on and team leadership experience, ensuring smooth front-end to back-end integration. .NET Core & Angular: Implemented various data visualizations using D3.js, integrated complex APIs, and developed dynamic, responsive applications. Azure Logic Apps & SharePoint: Built multiple workflow automation solutions; also familiar with PowerApps development. Salesforce Development: Developed Apex triggers to interact with MSSQL via custom .NET APIs. Created Visualforce pages to fetch and display external API data. Performed CRUD operations on both standard/custom Salesforce objects. Conducted R&D on Salesforce Flows for automation (with some custom object limitations). I bring a full-lifecycle development mindset and enjoy solving real-world business challenges through code. Looking forward to hearing from you! Thanks!

@maximg10

⭐Hi, I’m ready to assist you right away!⭐ I believe I’d be a great fit for your project since my experience in C#, SQL, .NET, and API development aligns perfectly with your requirements. With a proven track record in software engineering, I have successfully implemented RESTful APIs using modern .NET approaches and handled XML serialization efficiently. I specialize in developing clean, asynchronous API calls via HttpClient, ensuring clear error handling, and creating concise helper classes for streamlined future endpoint additions. Additionally, I have expertise in SQL Server, enabling me to seamlessly integrate the data layer with external accounting services through REST-style APIs and generate FA(3) KSeF-compliant XML invoices. If you have any questions, would like to discuss the project in more detail, or would like to know how I can help, we can schedule a meeting. Thank you. Maxim

@uzzairkhan

You need a clean .NET data layer that syncs invoices with external accounting APIs and exports KSeF ready FA(3) XML from SQL views. My approach focuses on a small, testable integration layer built around async HTTP clients and clear request boundaries. I structure helpers so each endpoint maps cleanly to GET, POST, or PUT calls with consistent authentication and error handling. This keeps future provider additions predictable and low risk. For exports, I generate FA(3) compliant XML directly from your SQL views using strongly typed models and XML serialization. The output validates against the official XSD so uploads to KSeF work without manual correction. This scope fully covers the described API communication and invoice export flow. I will flag any edge cases or schema gaps early before they affect delivery. I recently delivered a similar XML export module that passed third party schema validation on first submission and required no post upload fixes. Do you already have the FA(3) XSD version locked, or should the exporter support easy schema updates later.

@mkh559a5a1fd66e9

I will build a clean, maintainable integration layer that precisely meets your accounting workflow needs. The solution will leverage modern .NET 8 with a focus on clean separation between API communication and XML generation. For the REST API integration, I'll implement a provider-agnostic service using HttpClientFactory with Polly for resilient connections. The core will be a generic `AccountingServiceClient` handling GET, POST, and PUT operations with proper authentication flows for InFakt and Betterfly. Each provider gets a dedicated adapter ensuring future additions are straightforward. The KSeF export module will use LINQ to SQL against your views, transforming data into FA(3)-compliant XML via XmlSerializer with explicit schema validation. The exporter will include pre-upload XSD validation, eliminating manual fixes before KSeF submission. Stack: .NET 8, Entity Framework Core for data access, XmlSchemaSet for validation, and Serilog for monitoring. Configuration will be environment-ready with JSON settings for endpoints and credentials. Delivery includes full source, provider setup, and validation proof showing successful XSD compliance. The code will be production-ready with comprehensive unit tests. My project, Not same but related to xml generation against schema: https://www.freelancer.com/projects/optical-character-recognition/LLM-Mixed-PDF-XML-Converter/details Drop me a message and lets have a short conversation to proceed it to finish as soon as possible.

@saadrizwan97

As an experienced developer rooted in the .NET framework, SQL databases, and API integration, I'm more than ready to take on your C# SQL API & XML Export project. My proficiency in C# and databases like SQL Server make me a dedicated go-to person for the efficient synchronization of your data layer with external accounting services using REST-style APIs as you've outlined. Using HttpClient or other modern .NET methods, I'll ensure not just clean, but asynchronous calls with clear error handling, key for efficient future endpoint additions.

@jagratip3

Hello, This project aligns perfectly with my experience building clean, enterprise-grade integration layers and XML exporters in C#. I can deliver a fully asynchronous, maintainable solution that communicates reliably with external accounting services while generating KSeF-compliant invoice exports. Proposed Approach (MVP-first) API Integration Layer: REST-style HTTP calls using HttpClient with GET, POST, and PUT only Asynchronous, thread-safe operations with proper error handling Helper classes and configuration that allow easy addition of future endpoints Invoice Exporter: Collects relevant rows from your SQL views Generates FA(3) KSeF-compliant XML files Validates output against official XSD schema for direct KSeF upload Deliverables ✔ C# source code for API integration layer ✔ C# exporter producing KSeF-compliant XML invoices ✔ Sample configuration and validation proof Acceptance Fit Fully asynchronous API calls with clear error logging Clean, modular, and well-commented code Sample invoices validated against XSD schema Ready for immediate integration with your SQL Server views I am confident I can deliver this module quickly and cleanly, providing a maintainable foundation for future endpoint expansions or export requirements. Best regards,