Margin alerts basically mean that you bought shares with borrowed
money (a loan).  The stock itself and/or other holdings are the
collateral.

Now that the shares are much lower than your purchase price, they want
money to secure/repay the loan.

This is, of course, extremely bad for you.  You'll need to come out of
pocket to satisfy the margin call.  Otherwise, they'll liquidate the
security and take what they need.

Margin and leverage are risky propositions.

-Rob