Paginated Reports Embed : getting error "PowerBIEntityNotFound" on GenerateToken

Hello - 

I'm trying to embed Paginated reports in an application for customers (App owns data).

I've Premium P1 Capacity. Report is deployed in new Power BI Premium Workspace. 

I've created Azure AD Web App with ServicePrincipal.

I'm testing the embed API in Postman as below steps. 

1. Get Azure AD Bearer Token - https://login.microsoftonline.com/<<tenantid>>/oauth2/token

 2. Generate Token - https://api.powerbigov.us/v1.0/myorg/groups/<<workspaceid>>/reports/<<reportid>>/GenerateToken < --- I get below error message.

I made sure that I've correct Report ID and Workspace ID.

{
    "error": {
        "code": "PowerBIEntityNotFound",
        "pbi.error": {
            "code": "PowerBIEntityNotFound",
            "parameters": {},
            "details": [],
            "exceptionCulprit": 1
        }
    }
}

Am I missing anything here specifically for Paginated Reports? 

 Thank you