Cant access /groups/{group_Id}/reports/{report_id}/GenerateToken

Could you please share the error details?

See if the following thread helps:

Get Report details API responds with 400 bad request

Regards,

Michael

For me it was because I was missing the datasetId parameter in my request body like the example at https://msdn.microsoft.com/en-us/library/mt784614.aspx shows

{   
    "accessLevel": "View",
    "identities": [     
        {      
            "username": "EffectiveIdentity",
            "roles": [ "Role1", "Role2" ],
            "datasets": [ "fe0a1aeb-f6a4-4b27-a2d3-b5df3bb28bdc" ]
        }   
    ] 
}