Here is my replies to your queries:
1) In case you have provided the goods or services to the client but haven't made any invoice and haven't received any payment yet, as per the provisions of GST Act, you are not supposed to make the payment as the invoice is not raised yet. As per the provisions of GST Act, GST to be paid on 20th of the next month in regard to all the invoices generated in the previous month.
So, in your case no invoice means no GST.
2) In case of income tax, you will record the transaction only when you will generate the invoice and if there is no invoice it will not be recorded n your books of accounts. In income tax act there is provision to book income and if not recoverable you can simultaneously book bad debts so there will be no tax on the income booked. But if you book the income means raise the invoice GST should be paid. So i suggest just avoid the transaction if you are 100% sure that you will not receive the payments.
I hope your queries are resolved.
Let me know if you have any other query regarding the same!
Thanks and Regards