Rectification of GSTR- 3B

 1) Are this retrun both GSTR1 and GSTR 3 are for the month March 21 ? 

 2) What is the reason for Debit  Note  issued  by  the  Supplier ?. 

 3)  please  elaborate  in details . 

1) Debit notes raised by you cannot be uploaded as part of GSTR1. If you have already done that, you can reverse the entry when you file GSTR1 for the subsequent tax period.

2) Also ask your vendor to raise a credit note (in respect of the debit note) and upload the same.

3) As far as GSTR3B is concerned, you are required to reverse the input tax credit to the extent of debit note (by manually reducing the ITC). Once the vendor uploads the credit note, ITC mismatch will be taken care of.