Dear Sir A firm is engage in the business of labour supply to his client by deploying manpower from contractor with predifined margin. On the basis of record with client ( attendance record etc.), firm is raising the periodic Bills (GST TAX INVOICE)to his client and paid GST accordingly after taking the Input Tax Credit from his contractor. In summary the business model is - Input from Contractor + Own Margin = Output Service to Client The query is If the Firm is raise Output Service Bills without Input Service ( By way of proper Tax Invoice from Contractor) and recognise his revenue and to math the revenue estimated expenditure is also provided for the month and after receiving the actual Tax Invoice from ( after 1-2 months ) Contractor claim ITC. For ex. In April Output Service Rs. 100 Lakhs, Input Nil In June Output Service Nil , Input Rs. 80 Lakhs Is there any violation of GST provision by following above practice ? Whether Month to Month booking is mandatory under GST Law ?