Getting forbidden error when trying to export report to PDF

I'm trying to use the API to export a report that's being embedded into one of our applications, however I keep getting a Forbidden error, however I know my authenticaion mechanism is fine as I can do other stuff via the API like refreshing reports, generating embeed tokens etc.
  
I read somewhere that it might be due to my user accounts subscription tier (Pro). Can anyone here confirm if I need to go Premium to access this functionality?

Here is the code in case you're wondering what I'm doing

public async Task<string> ExportReport(Guid groupId, Guid reportId, FileFormat format)
    {
      var authenticationResult = await _authContext.AcquireTokenAsync(_resourceUrl, _credential);
      var tokenCredentials = new TokenCredentials(authenticationResult.AccessToken, "Bearer");
      using (var client = new PowerBIClient(new Uri(_apiUrl), tokenCredentials))
      {
        var request = new ExportReportRequest(format);
        // this line below is where I get the forbidden
        var export = await client.Reports.ExportToFileAsync(groupId, reportId, request);
        var result = await PollExportRequest(client, reportId, groupId, export.Id, 5);
        // rest of the code ommited for brevity 
      }
    }

any help would be greatly appreciated.