Here are some information on Bad Debt if you are getting stuck.
A bad debt situation occurs when money that is owed cannot be recovered. You can apply for bad debt relief from the Comptroller of GST for return of the output tax previously accounted for and paid by you.
On the other hand, if you as a customer have not paid your supplier within 12 months from the due date of payment, you are required to repay to the Comptroller the input tax that you have previously claimed (if any). For more details, please refer to If I have claimed GST before paying my supplier
For more information you may visit: https://www.iras.gov.sg/IRASHome/GST/GST-registered-businesses/Working-out-your-taxes/Common-scenarios/Customer/Bad-Debt-Relief/
Have more questions regarding Bad Debt? Feel free to ask below!