In general, if you would like to deposit funds, the amount has to be equal to the margin call amount. If you choose to liquidate your stocks to cover the call, the amount you have to sell should be equal to the margin call amount divided by the minimum maintenance requirement. (Firstrade)

If the customer’s account falls below the required minimum balance, the brokerage may not always issue a margin call to the customer, requiring them to top up the account. Instead, they may sell part of the customer’s securities to restore the margin account to the maintenance margin without notifying the customer. (Corporate Finance Institute)

Margin calls originally got their name because the brokerage would call the trader on the telephone. Your brokerage may or may not still conduct margin calls via phone call. Your brokerage may also automatically close certain positions after a margin call has been issued. (the balance)