Hello Venkatesan, Ashokkumar,
Welcome to the Microsoft Q&A forum.
It seems like the managed private endpoint has not been created, or It is not approved yet.
As a troubleshooting step, please run the below PS command to check the DNS resolution.
Resolve-DnsName yourfunctionapp.azurewebsites.net
If the PE is created and approved, you will see "Privatelink"(privatelink.azurewebsites.net) in the NameHost section.
Example screenshot for blob storage.
You will see "Privatelink" in the NameHost section for the function app.
Please see this reference document.
Understand private DNS zones:
https://learn.microsoft.com/en-us/azure/azure-functions/functions-create-vnet#understand-private-dns-zones
I hope this helps.