SSRS subscription report CSV format not working

I have SSRS subscription reports I want to generate report in CSV format but SSRS is erroring when I assign CSV. There is no problem with PDF and XLS format. Is there any alternatives to get CSV reports?

This is the code snippet that loop through Subscrtion Parameters

 rs.GetSubscriptionProperties(SubscriptionID, extSettings, desc, active, status, eventType, matchData, ParamSubScription)

 extensionParams = extSettings.ParameterValues

 For Each extensionParam In extensionParams
                                    rpname = CType(extensionParam, ParameterValue).Name.ToLower()
                                    rpvalue = CType(extensionParam, ParameterValue).Value
                                    If rpname = "render_format" Or rpname = "renderformat" Then                                      
                                            CType(extensionParam, ParameterValue).Value = "CSV"

                                      End If

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