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                   55062 Points
                   Joined June 2017
                
               
			  
			  
             
            
             Dear Sanjeev
What do you mean by "Rate fluctuation" ...... If it means ie instead of 18% you charged 12% , then you are liable Pay interest .
if ,we read Section 50 of CGST it's clearly states that " Every person who is liable to pay tax in accordance with PROVISION OF THIS ACT but fails to pay "
so you have not paid the tax to Govt as per provision of Act or short paid , hence liable to pay interest  @ 18%