Whats the implications of defaulting on your transaction? I...

Whats the implications of defaulting on your transaction?

I unfortunately had a margin loan for some stocks including MFS, I thought it was a great bargain at the time to pickup a few at $2. Well the rest is history but I didn't have enough money in my account to settle the transaction since the lender cancelled the LVR on that stock. My broker told me I had to top up my account or it wouldn't settle...

Simply not settling sounded too good to be true but I topped it up anyway.

I'm still not sure what would have happened if I didn't.