How to Update SQL Table Where condition is True - php

Question

PROBLEM: I am trying to UPDATE table data with a "forgot password key" where the email field matches the user's form input on a previous page.
I want to make sure the user's input is sanitized and a match can be found in the database.
ERROR: The code does not update the ForgotKey Field in my Database
Here is my code, error is happening on line 7 where stated in the comment.
$ForgotKeyLength = 9;
$ForgotKeyString = "123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
$ForgotKey = substr(str_shuffle($ForgotKeyString), 0, $ForgotKeyLength); //shuffle String, start with 0, 9 characters long
$sql = "UPDATE UserTable SET ForgotKey = ".$ForgotKey." WHERE Email = ? ";
$stmt = mysqli_stmt_init($conn);
if (!mysqli_stmt_prepare($stmt, $sql)) {
header("Location: ../forgot.php?error2"); // THE ERROR HAPPENS HERE, UNABLE TO PREP STATEMENT
exit();
}
else {
mysqli_stmt_bind_param($stmt, "s", $Email);
mysqli_stmt_execute($stmt); // I believe this line should update the table
$result = mysqli_stmt_get_result($stmt);
if ($row = mysqli_fetch_assoc($result)) {
//success: send user their email from here
$variable = $row['Email'];
}
else {
header("Location: ../forgot.php?error5");
exit();
}
}