Error 431, while accessing mock API

Questions
1

HI I am using blizrock/kong-oidc-keycloak dockerfile opensource for the installation of kong.
Also i am using keycloak as IdP. Testing an Authorization flow, i am accessing in incoginito chrome brower http://IP:8000/mock

it is showing error :
" This page isn’t working

If the problem continues, contact the site owner.

HTTP ERROR 431"
Anyone please help me if you find anything

2

The error, 431 Request Header Fields Too Large, might be addressed via this setting to increase the allowed header size in the request.