Can I start a fresh series of serial number for my ‘invoice’ or ‘bill of supply’ every day, e.g., 20160401-001 for April 1st and 20160402-001 for 2nd April

The invoice rules require that the serial number should be consecutive and unique for a financial year. Hence, restarting the serial number of the invoice or ‘bill of supply’ on a daily basis would not be considered appropriate.

(ICAI FAQ PUBLCATIONS 06-09-2017 TAX INVOICE, CREDIT AND DEBIT NOTES: FAQ NO. 42)