Power BI Generate Token API Failure

[skumar_allturna]

Hi
We have created a MVC web API with embedded Power BI reports. We have also commissioned a Power BI dedicated capacity on Azure.  The app was being used successfully for the last 4 months - however we now have an API Failing - https://api.powerbi.com/v1.0/myorg/groups/{groupId}/reports/{reportId}/GenerateToken

The flow of the Power BI API is as follows. 

https://login.microsoftonline.com/common/oauth2/token - Request an access token - POST Successful

https://api.powerbi.com/v1.0/myorg/groups - Get groups - GET Successful

https://api.powerbi.com/v1.0/myorg/groups/{group-Id}/reports - Get reports in a group - GET Successful

https://api.powerbi.com/v1.0/myorg/groups/{groupId}/reports/{reportId}/GenerateToken - Generate Token for POWER BI Embed control - GET Fails.
The body passed for the GenerateToken function is
{
 "accessLevel": "View"
}

However the response is

{

    "error": {

        "code": "Unauthorized",

        "message": "User is not authorized"

    }

}

This was working for almost 3 months and we haevnt changed any permissions on the user. Infact we have as part of our testing/trouble shooting  efforts allocated all Power BI permissions in Azure Application setup.

I cant figure out what could have changed. Any directions as to where we should be looking/trouble shooting? Appreciate any help

Regards
Sid