Input reverse

srikumar (audit staff) (1203 Points)

10 January 2020  
sir, in the year Apr, may 2019 my client purchase goods from some one party. but still the date such party not filling gst 1, so input not available at gst 2a, now i have reverse such itc amount along with interest at gst 3b.

my doubt was interest how much sir?
interest mandatory to pay at gst 3b or after notice issued by dept?
how to calculate interest amount ? sir pls explain