How to use Keyword Query Language (KQL) query to limit search scope to a particular sub path of a public web site

Question

Requirement: On a SharePoint Online site, use custom search vertical to display search result from a sub path of the cooperate public site.

What has been done:

1, Created a Microsoft Graph Connector to the public web site https://abcefg.com

2, On the SharePoint Online site level, created a custom vertical using the above connector as content source, in the Query section of the vertical, add KQL query to limit the search result to the sub path of the public web site

I have tried the following KQL queries but none worked.

path:https://abcefg.com/d88

path:https://abcefg.com/d88/

I used reference here

https://learn.microsoft.com/en-us/sharepoint/dev/general-development/keyword-query-language-kql-syntax-reference

I would appreciate any help on this. Thanks