在PHP中清除回显消息

I have a text box in which the user can start typing the name of a company and it will start listing the companies to choose from. The problem I am having is that if I click ENTER with empty box it gives the message "Please enter a stock" but then when the user starts typing the previous message stays there and the suggestions are also shown. How do I remove the previous message? This is the page

if($_SERVER["REQUEST_METHOD"] == "POST"){

    $stock = lookup(strtoupper($_POST["symbol"]));


    if(empty($_POST["symbol"])){

        echo"You must enter a stock symbol";
        exit;

    }else if($_POST["symbol"]){

    $price = number_format($stock['price'], 2);

    echo "A share of {$stock['name']} costs $price";
    }

}

else{

    // render portfolio
render("stock_search.php", ["title" => "Get Quote"]);
}

You should hide or clear the suggestions with JavaScript on (re-)start of typing.

you suould redirect to page so that the page refreshes and message removes

if($_SERVER["REQUEST_METHOD"] == "POST"){

$stock = lookup(strtoupper($_POST["symbol"]));


if(empty($_POST["symbol"])){

    echo"You must enter a stock symbol";
    //use redirect method to move page or refresh the same page not use exit; 

}else if($_POST["symbol"]){

$price = number_format($stock['price'], 2);

echo "A share of {$stock['name']} costs $price";
}

}

else{

    // render portfolio
render("stock_search.php", ["title" => "Get Quote"]);
}