for FY 2019-20 invoice series is from BR12019-20 to BR1002019-20 then in FY 2020-21 invoice start series from BR1/2019-20 , this FY 2020-21 is considered as unique series in GST? it is called unique invoice?
Yes it's unique series. In term of Rule 46(b) it should be unique for Financial Year. for Example in 2020-21 If Serial no. R001 is started it cannot be repeated in Fy , but same can be again started from 2021-22
That means for example invoice number for FY 2019-20 is BR12019-20 and invoice number for FY 2020-21 is BR1/2019-20, each of this invoice are unique, am i right? main diffrence two this series there is special character slash("/")