Advance/deposit is not a consideration as per definition of 'consideration' under Section 2(31) of CGST Act. Advance/deposit becomes consideration when goods or services are supplied. Advance/deposit is always subject to final adjustment.
Section 2(31) of CGST Act “consideration” in relation to the supply of goods or services or both includes -
any payment made or to be made, whether in money or otherwise, in respect of, in response to, or for the inducement of, the supply of goods or services or both, whether by the recipient or by any other person but shall not include any subsidy given by the Central Government or a State Government;
(a) the monetary value of any act or forbearance, in respect of, in response to, or for the inducement of, the supply of goods or services or both, whether by the recipient or by any other person but shall not include any subsidy given by the Central Government or a State Government :
(b) Provided that a deposit given in respect of the supply of goods or services or both shall not be considered as payment made for such supply unless the supplier applies such deposit as consideration for the said supply;
Thus until or unless supply is made against this advance, it is not Govt.’s money. It is your option either to apply for refund or adjust the advance against the same party for another transaction/deal.
Regarding unjust enrichment and making payment through Electronic Credit Ledger legal position is as under :-
Tax-paid character is same whether paid in cash or through Electronic Credit Ledger. Your purchase invoices (tax paid) are equal to cheques. Credit lying in your ECL is your money subject to eligibility for usage.
Unjust enrichment is not involved.
I agree with replies of Sh.Venkatprasad Ji and Sh.Ganeshan Kalyani Ji at serial no.5 and 6 respectively. Circular no. mentioned by Sh.Venkatprasad ji gives different scenarios and is helpful to the querist.