Hi , @Sabarikarthy
According to your description, you are call the Power BI Rest API in Power Automate but you get the error as no pbi entity found.
First , we need to check if you can run successfully in the official document "Try it ":
Groups - Get Group Users - REST API (Power BI Power BI REST APIs) | Microsoft Learn

If this fails, you need to check if you have the corresponding permissions, or if you have obtained the correct workspaceid. The Workspace ID is here in he url:(If you're still reporting an error here, you may need to contact the appropriate Power BI technical support)

If you succeed here, but Power Automate still fails, you need to check that your token is getting it correctly.
Test method: Use the Postman tool to test your Power BI Rest API and use the token you generated to test whether the API can be successfully called.
And also you need to check if your token has the Workspace.Read.All or Workspace.ReadWrite.All permission.
And i test it in my side , i works good like this:

If your call to the Power BI Rest API in Postman also fails, then you may want to consult the relevant Power BI technical support to check if your token permissions are insufficient.
Best Regards,
Yueyun Zhang