i created a testing vendor account for testing. while i tried to cashout, the total available balance was 1930, but i entered 3000 in the withdrawal and clicked submit button,.. surprisingly the withdrawal request was submitted successfully. after that that vendors account current balance gone to negate -1070,
still i tried to make another withdraw while in negative balance (-1070) , i entered another 3000 in the withdrawal(this was the 2nd request) and clicked submit button, the second request was also submitted successfully.
This is intended feature - vendor is allowed to make a withdrawal that will cause his balance to go to negative value, as well as he can make a withdrawal when he already is on negative balance. It was implemented probably to let vendor take a loan from administrator.
The built-in addon "Vendor debt payout" allows you to block vendor's administration panel, when he reaches certain amount of debt.
We can also make a custom modification for you, which will block the withdrawal request if it causes balance to go below 0, and will completely hide withdrawal button if balance already is below 0. If you'd be interested, PM me so we can make more detailed specification.