REG FOR NEW RC - ARN only received

ARN is a very different number from GSTIN. ARN is an identification number for your application. It may or may not get approval.

Yes you can issue bill by mentioned ARN therein, but Receptient would not be eligible to claim ITC on same . Infact in term of subsection (3) of Section 31 of CGST , you can issue Revised Invoice within 30days from date of issuance of GSTN by putting your GST no. therein for all those invoices you have issue during the period effective date of registration till date of issuance of certificate.

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