I filed monthlyGSTR1 and 3B for Apr20 - Dec20 (9 months).
Then I opted for Quarterly and filed March 21( left Jan'21 and Feb'21 as they are optional).
I get this error while I tried to file GST Annual return for 20-21
"To file your annual return, filing of all GSTR-1 and GSTR-3B returns are mandatory. File your pending GSTR-1/3B return(s) and try again"