When submitting a Core 3.1 form with a long text field I am getting:
HTTP Error 404.15 - Not Found The request filtering module is configured to deny a request where the query string is too long. Most likely causes: Request filtering is configured on the Web server to deny the request because the query string is too long.
I've searched through older answer, but did not find anything specific to core 3+.
Make sure you HTML form has method="post" on it. In other words, you need to make the request (submit the form) via POST, not GET, so that the values go in the request body, not the query string (i.e. URI).
what is the type of action that you are submitting the form to - is it HttpGet or HttpPost? if its HttpGet, then querystring has certerain limitation varies from browser to browser. Please refer this link What is the maximum possible length of a query string? for detailed information on this.
With that being said, in general, if querystring exceeds the lenght that it can handle, HttpPost is used even which does not impose any such limitations.
If you post the code both view and controller action, then we can assist further.
