Hi Richa!
Don’t know the details of this. But If I’m not wrong,
• This could be because there are highly similar pages on the website that Google sees as duplicate. And, it didn’t choose the URL which you may have set as canonical.
• This is common in e-commerce sites that have same products with different attributes, that seem similar to bots. Or, if a site chooses HTTP URL over HTTPS one which isn’t favoured by Google.
• You can go through the list of URLs in the coverage section and inspect them. Also, a fix that you can explore is adding self-referencing canonical tag, do some serious interlinking for the page, and see if there are ways you can make the content unique so Google no longer sees it as duplicate.