Applicability of E Invoice credit note under GST

bipin (accountant) (115 Points)

12 January 2021  
we have applicable for e invoice after 1 jan 2021. we issued the tax invoice in june 20 and customer has return the material in oct 20 which are received to us in jan 21

1)can we taken it as a sales return in gstr1
2) canxwe reduce the liability in gstr1 month of jan 21
3) e invoice required if we credit note book in jan 21