In the month on aug-21 we had issued sales wrongly with lesser amount. Is there anyway to increase the value?.(balance amount) Has we have already filed Gstr-1 for the month.
Yes he can. Provided that the seller is charged less in original invoice it self. For ex:- I am the seller and had issued original invoice physical copy of 10k and same was updated in portal, I later realised that I charged less so I can issue a debit note. If it's merely an typing error in GST portal then amending invoice would be sufficient