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The law provides that, if you have taken registration within 30 days of being liable to be registered, then your registration is effective from the date you were liable to be registered.
So in that 30 day period in between, initially you would have issued non GST invoice, but after getting the registration certificate, now you can issue revised GST invoice for those invoices issued in those 30 days.
1. The invoices from April 2020 to Dec 2020 when your turnover was <20L.
2.You need to file returns only for the invoices you raise from the date you get the GSTIN.
3. For entire FY.
We may assist you in entire GST compliances & filings.
It is advisable to take a phone consultation for detailed discussion.