As per Sec16(4), the CGST Act 2017,
A registered person shall not be entitled to take input tax credit in respect of any
invoice or debit note for supply of goods or services or both after the due date of furnishing
of the return under section 39 for the month of September following the end of financial year
to which such invoice or invoice relating to such debit note pertains or furnishing of the
relevant annual return, whichever is earlier.
so that means we cannot take credit after Sep'19 for the invoices of 18-19..