reverse of output liability

Am toh patel (75 Points)

18 May 2018  
I sale to mr X 50000 on credit and issue tax invoices against sale and I paid 9000 igst on sale.mr X not payment till date.

1.whether any time limits of received payment against invoice of sale ?

2.what I do subsequently, if sale is cancelled and what are the treatment is required for it ?

3.in which case I can revert the amount of output tax liability ?