@Urja Patil Custom search API or the portal is designed to provide a custom search experience based on searching a particular domain/s. This does not include the entire bing search API response if no allowed list entry is provided.
You can use the bing web search API along with filters and advanced syntax to limit the results from a certain site. For example, every result from bing search API can be parsed to check for sites that you do not want to display the result and exclude them in your application or UI.
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