No return from sqli_query for login [duplicate]

This question already has an answer here:

• mysqli_fetch_array()/mysqli_fetch_assoc()/mysqli_fetch_row() expects parameter 1 to be resource or mysqli_result, boolean given 33 answers

I have a login page that redirects to this set of PHP code:

<?php
   $mysql_host = "***";
   $mysql_database = "***";
   $mysql_user = "***";
   $mysql_password = "***";

   $conn=mysqli_connect($mysql_host, $mysql_user, $mysql_password, $mysql_database);

   if (mysqli_connect_errno($conn)) 
   { 
       echo "Failed to connect to MySQL: " . mysqli_connect_error(); 
   }

   $email = $_POST["email"];
   echo $email;
   $password = $_POST["pass"];
   echo $password;

   $stmt = $conn->prepare("SELECT email, password FROM account WHERE email = ?");
   $stmt->bind_param("s", $email);
   $stmt->execute();
   $stmt->bind_result($mail, $pass);
   echo $stmt;
   echo $mail;
   echo $pass

   if ($pass === $password and $password != null)
   {
       echo "Logged in";
   } else {
       echo "Unsuccessfull";
   }
?>

When I run it with the test values in my database I get these messages:

random@sample.com

password

SELECT password FROM account WHERE email = random@sample.com

Warning: mysqli_free_result() expects parameter 1 to be mysqli_result, boolean given in /home/a3996154/public_html/login.php on line 22

Unsuccessfull