GST liability

Taxable

But it doesn't include in the definition of supply..
can you explain with provision

Sec.7 supply is a wider term and inclusive definition.

It includes all forms of supply...
And forfeiture of advance amount is absolutely in/during the course of business

Hence taxable.

Also please elaborate your query

Thank you

Yes, supply is wider term and inclusive definition but as per sec 7,for supply there must be supply of either good or service but in this case there is no supply of either goods or services so how it fall in the definition of supply

Firstly you might have received the advance amount against supply of service.
(no tax at the time of advance receipt against supply of goods)

Further, the same should be shown in P&L A/c as business income only and can not offer as other income.

Further more, it can not be ignored the origin nature of the transaction.

And it is the income against the forfeiture of supply of service in the course or furtherance of business.

Hence taxable.

Advance received against the goods in not taxable because as notification 66/2017. Where as in case of supply of service it is liable to pay tax against the advance please refer section 13 of CGST Act 2017 for more clarification