C# Tally XML Integration DLL

I need a clean C# class-library (targeting .NET Framework 4.0) that will later plug straight into our main solution and handle two jobs for both TallyPrime and ERP 9:

• convert our existing XML data (every column already fixed and agreed) to well-structured JSON, and
• push that same XML directly into Tally.

To demonstrate the DLL you will also supply a lightweight WinForms test harness. The form shows a single dropdown pre-populated with four values—B2B Purchase, B2B Sales, B2C Purchase, B2C Sales—plus two buttons: “Generate XML → JSON” and “Import XML to Tally.” When I click either button I should see a success/failure message; for the import button I also expect any error text returned by Tally.

Inside the DLL I want one public façade class exposing methods such as GenerateJson(string xmlPath) and ImportToTally(string xmlPath, string companyName). Feel free to add supportive utility classes, but keep the external surface minimal. All mapping from our XML columns to Tally’s tags must be exact and covered with clear inline comments or a separate mapping document so maintenance remains simple.

Acceptance will be based on:
• Test form running without extra configuration on a vanilla Win 10/11 machine with .NET 4.0 runtime.
• Successful JSON output that mirrors the source XML values one-to-one.
• Seamless import into both TallyPrime and ERP 9 instances provided during review.
• Clean, readable C# code and a compiled DLL ready to drop into our primary project.

If you have tackled Tally integration before, especially with its XML gateways, please mention it—otherwise a brief plan on handling company selection, port settings, and security would be helpful.