Mismatch in tds and gst return

A dealer supplies to a government department in 20-21 and his payment comes after deducting gst tds but the payment has come in 21-22 and is visible in 21-22 of the Gst tds return and the officer has issued a notice on the same. It has been said that the sales have been less in 21-22 but the sales are already added in 20-21 return.Now please tell me what to answer on this.