Hi Mhabub,
Hopefully you were able to fix your issue, but the docs here may be able to help you out.
I’ve not had the chance to use a sandbox account yet, so I’m unsure if it works the same. But, you may need to ‘publish’ your search configuration for your changes to take affect. I ran into a similar issue when I added a new vertical but forgot to publish the newest version. In your search experience, go down and select ‘Configuration Labels’ to change which version of your experience is published. You may need to adjust your PRODUCTION label to point to your latest stable version.
Hope this helps!