As per Section 73(5) or 74(5)
5) The person chargeable with tax may, before service of notice under sub-section (1) or, as the case may be, the statement under sub-section (3), pay the amount of tax along with interest payable thereon under section 50 on the basis of his own ascertainment of such tax or the tax as ascertained by the proper officer and inform the proper officer in writing of such payment.
Before Issuance of Notice in Form DRC-01 under section 73(1) of CGST ACT can self ascertain the tax liability and pay the same vide DRC-03.
While paying the same the dealer may utilize the Credit ledger or cash ledger..
It is mandatory to utilize the cash ledger only to pay the liability as ascertained at the time of Annual Return..