This discussion clarifies whether Reverse Charge Mechanism (RCM) applies to sundry debtors when a GST demand notice is issued. The consensus is that RCM is generally not applicable in this scenario, especially if the seller has already paid the GST on the invoiced amount via GSTR-3B. The department's demand might stem from a misunderstanding or an issue with how outstanding debtors are reflected in the balance sheet. It's advised to provide proof of GST payment and potentially seek professional advice from a CA for a proper response to the department.