I think that’s the default for any brokerage product. However, when you apply for options trading, you have the option to add margin to your account. It’s esse

I think that’s the default for any brokerage product. However, when you apply for options trading, you have the option to add margin to your account. It’s essentially just a tick box. It appears from the twitter thread that this user unknowingly added margin to his account, traded on margin, then had a really big margin call.