Automate .NET web Form submission

I have a transaction form running on a .NET-based site that needs to submit itself automatically once all order details have been populated. Manually clicking the “Submit” button is no longer an option for the workflow I’m building, so I’m looking for clean, well-documented code that will handle the submission event in the background while still respecting the server-side validation already in place.

Here’s what I’m after:
• A lightweight C# / JavaScript snippet (or a blend of both) that detects when the required order-detail fields are complete, programmatically posts the form, and gracefully handles any validation errors returned by the server.
• Clear instructions on where to drop the code within the existing .NET page or user-control structure.
• A simple way to extend or modify the field mappings later, so I’m not locked into hard-coded names.
• Confirmation that the solution works in modern browsers without relying on deprecated APIs.

Acceptance criteria
• On entering valid order details, the form submits automatically and the server receives the payload exactly as if a user had clicked “Submit.”
• No client-side console errors and no disruption to the styling or layout of the page.
• Code comments explain each functional block in plain English.

If you’ve automated form submissions on .NET sites before and can deliver a tidy, testable snippet, I’d love to review your approach.