Fix: Razor Pages Handler Not Found 404 Error

The Error

POST to page returns:

404 Not Found

Quick Fix - 1 Min

1. Handler method must be public async Task<IActionResult> OnPostAsync(). 2. Form must have asp-page-handler="YourHandler". 3. Check @page "{handler?}" if using route.

Root Cause

Razor Pages matches handlers by naming convention. Method private or misnamed = 404.