For billing serious

you have to follow CGST rules 2017 section 46 sub section b 

Yes u can , should not be more then 16 digit

Yes... You can follow as per Your above said way. No more restriction. But, Don't be the same Series again...

yes , you can use this series ..

Rule for GST Invoice No.

1) Maximum 16-digit serial on each invoice that is unique for each financial year.

2) It can contain alphabets, numbers and special characters “-”and “/”.

thanks to all for your advice..

Originally posted by : Jayesh Bhagat
	thanks to all for your advice..

Most Welcome

46(b)insists only uniqueness within a financial year and not uniqueness in each financial year.So...You can start with invoice number 1 even without any prefix or suffix in each year or even continue the series used in last year.The same invoice number should not be repeated within a year.If you want repeat invoice number 1 that issued in April ,2018 in another month of 2018-19....you can do it by inserting any prefix or suffix