i remember correctly, someone swiped more than available balance, but that only worked for one time. next swipe, did not go thru because credit already -ve.

also, we dont know if bigpay has a limit/threshold to allow this to go thru (if possible), especially your example -- rm1k swipe with rm100 balance. maybe there is a small-ish % allowance to over-swipe.

well for me, my rm192 purchase didnt go through when my available credit was rm186

I think this depends on luck. I forget to top up when it charge for my GE insurance, it become -RM151.52 on my account.

Sometime people are just lazy to read the TnC...

https://docs.wixstatic.com/ugd/0156cb_0421e...3ef676007b2.pdf

You  should  frequently  review your Card Account  to check and verify your Available Balance before
using your Card. You must always ensure that there are sufficient funds in your Card Account to pay
for  each  transaction  and  to  cover  the  total  amount  transacted  on  your  Card  Account,  including
purchases,  recurring  transactions,  cash withdrawals,  fees and  other  charges. If  the  total amount in
your Card account is insufficient, your transaction will be declined and in the case of recurring declined
transactions,  you  would  have  to  make  your  own  arrangements  for  payment  with  the  recurring
merchant. If you have not paid any of the fees (as may be applicable), your Card cannot be used and
we will be entitled to block, suspend and/or to terminate your Card account.