PHP第二个标签不工作，怎么了？

当我试图注册一个用户名已经存在的用户时，它应该需要_ONCE（“registo.php”），但是它没有进入我的login.php，而是将标题位置重定向到“registo.php？p=registo？e=true”，所以问题出在“index.php”中，但我看不出有什么问题，有什么遗漏吗

register.php

index.php

（需要一次）registo.php

新效用登记处


登记册

首先，这是错误的

index.php？p=registo？success=1

。只有第一个问号被视为传入参数的指示。之后的每一个问号都被视为字面问号

 $query = "SELECT username FROM login WHERE username = '$user'";
        $result = mysqli_query($db, $query); 
        if (!$result) {
            echo ' Database Error Occured ';
        }

        if (mysqli_num_rows($result) == 0) {


$sql = "INSERT INTO `login` (`id`,`username`,`password`) VALUES (NULL, '".$user."', '".$pass."');";
if(!mysqli_query($db, $sql)){
    echo 'Não foi possivel salvar os dados!';
}else{
$_SESSION['message'] = 'success';
header("location: index.php?p=registo?success=1");

}
 }else{header("location: index.php?p=registo?e=true");}
 }else
 {
    echo 'Os campos não estão definidos!'; 
    }

<div class="container">
        <?php
         if ( isset($_GET['p']) && $_GET['p']=='registo' || isset($_GET['e']) && $_GET['e']=='true')
            {require_once "views/registo.php";
        }
         else{require_once "views/login.php";}



        ?>

    </div>

<center>
<div class="box_css">
<form class = "form-signin" role = "form" action = "register.php" method = "post" style="max-width:50%">
            <h4 class = "form-signin-heading">Registar um Novo Utilizador</h4>
            <input type = "text" class = "form-control" name = "reg_username" placeholder = "Nome de Utilizador"  required autofocus></br>
            <input type = "password" class = "form-control" name = "reg_password" placeholder = "Password" required>
            <button style="margin-top: 15px; margin-bottom: 15px;" class = "btn btn-lg btn-primary btn-block hvr-grow-shadow" type = "submit" name = "registo">Registar</button>
         </form>
         <a href="index.php" style="max-width:50%;" class="btn btn-lg btn-primary btn-block hvr-icon-back">Voltar</a>

         </div>

         </center>

You Should be pass parameters Like this:
Before : header("location: index.php?p=registo?success=1");
         header("location: index.php?p=registo?e=true");
After : header("location: index.php?p=registo&success=1");
        header("location: index.php&p=registoe=true");