How to fix my CRUD not working in Update PHP MSQL

I tried to implement CRUD in m website but I am able to make Create, Read and Delete. However, something went wrong during developing the Update function. Can anyone help me? I will provide the code below. The code is used to update the users information if the logged in person is an Admin. Thank you.

<?php
// Include config file
require_once "config.php";

// Define variables and initialize with empty values
$firstname = $lastname = $email = $address = $status = $level = "";
$firstname_err = $lastname_err = $email_err = $address_err = $level_err = $status_err = "";

// Processing form data when form is submitted
if(isset($_POST["id"])){
    // Get hidden input value
    $id = $_POST["id"];

    // Validate name-first
    $input_firstname = trim($_POST["firstname"]);
    if(empty($input_firstname)){
        $firstname_err = "Please enter a first name.";
    } elseif(!filter_var($input_firstname, FILTER_VALIDATE_REGEXP, array("options"=>array("regexp"=>"/^[a-zA-Zs]+$/")))){
        $firstname_err = "Please enter a valid first name.";
    } else{
        $firstname = $input_firstname;
    }

    //Validate lastname
    $input_lastname = trim($_POST["lastname"]);
    if(empty($input_lastname)){
        $lastname_err = "Please enter a last name.";
    } elseif(!filter_var($input_lastname, FILTER_VALIDATE_REGEXP, array("options"=>array("regexp"=>"/^[a-zA-Zs]+$/")))){
        $lastname_err = "Please enter a valid last name.";
    } else{
        $lastname = $input_firstname;
    }

    //Validate email address
    $input_email = trim($_POST["email"]);
    if(empty($input_email)){
        $email_err = "Please enter an email address.";
    } else{
        $email = $input_email;
    }

    // Validate address 
    $input_address = trim($_POST["address"]);
    if(empty($input_address)){
        $address_err = "Please enter an address.";
    } else{
        $address = $input_address;
    }

    // Validate access level
    $input_level = trim($_POST["level"]);
    if(empty($input_level)){
        $level_err = "Please enter an level.";
    } elseif($input_level == 'Admin'){
        $level = $input_level;
    }elseif($input_level == 'Customer'){
        $level = $input_level;
    }else{
        $level_err = 'Please choose from Admin or Customer';
    }

    // Validate status
    $input_status = trim($_POST["status"]);
    if(empty($input_status)){
        $status_err = "Please enter a status";
    }elseif($input_status == '1'){
        $status = $input_status;
    }elseif($input_status == '0'){
        $status = $input_status;
    }else{
        $status_err = "Please enter a valid status";
    }
    

    // Check input errors before inserting in database
    if(empty($firstname_err) && empty($lastname_err) && empty($email_err) && empty($address_err) && empty($level_err) && empty($status_err)){
        // Prepare an update statement
        $sql = "UPDATE users SET firstname=?, lastname=? address=?, email=?, access_level=?, status=? WHERE id=?";

        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "sssssii", $param_firstname, $param_lastname, $param_email, $param_address, $param_level, $param_status, $param_id);

            // Set parameters
            $param_firstname = $firstname;
            $param_lastname = $lastname;
            $param_address = $address;
            $param_email = $email;            
            $param_level = $level;
            $param_status = $status;
            $param_id = $id;

            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Records updated successfully. Redirect to landing page
                header("location: index.php");
                exit();
            } else{
                echo "Something went wrong. Please try again later.";
            }
            // Close statement
            mysqli_stmt_close($stmt);
        }else{
            echo mysqli_stmt_error($stmt);
        }
    }

    // Close connection
    mysqli_close($link);
} else{
    // Check existence of id parameter before processing further
    if(isset($_GET["id"]) && !empty(trim($_GET["id"]))){
        // Get URL parameter
        $id =  trim($_GET["id"]);

        // Prepare a select statement
        $sql = "SELECT * FROM users WHERE id = ?";
        if($stmt = mysqli_prepare($link, $sql)){

            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "i", $param_id);

            // Set parameters
            $param_id = $id;

            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                $result = mysqli_stmt_get_result($stmt);

                if(mysqli_num_rows($result) == 1){
                    /* Fetch result row as an associative array. Since the result set contains only one row, we don't need to use while loop */
                    $row = mysqli_fetch_array($result, MYSQLI_ASSOC);

                    // Retrieve individual field value
                    $firstname = $row["firstname"];
                    $lastname = $row["lastname"];
                    $email = $row["email"];
                    $address = $row["address"];
                    $level = $row["access_level"];
                    $status = $row["status"];
                } else{
                    // URL doesn't contain valid id. Redirect to error page
                    header("location: error.php");
                    exit();
                }

            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }
        }

        // Close statement
        mysqli_stmt_close($stmt);

        // Close connection
        mysqli_close($link);
    }  else{
        // URL doesn't contain id parameter. Redirect to error page
        header("location: error.php");
        exit();
    }
}
?>

<?php
// core configuration
include_once "../../config/core.php";

// check if logged in as admin
include_once "../login_checker.php";

// set page title
$page_title = "Update Record";

// include page header HTML
include '../layout_head.php';

echo "<div class='col-md-12'>";

// get parameter values, and to prevent undefined index notice
$action = isset($_GET['action']) ? $_GET['action'] : "";

// tell the user he's already logged in
if ($action == 'already_logged_in') {
    echo "<div class='alert alert-info'>";
    echo "<strong>You</strong> are already logged in.";
    echo "</div>";
} else if ($action == 'logged_in_as_admin') {
    echo "<div class='alert alert-info'>";
    echo "<strong>You</strong> are logged in as admin.";
    echo "</div>";
}

echo "</div>";

//content when logged in
?>
<div class="wrapper" style="width: 500px; margin: 0 auto;">
    <div class="container-fluid">
        <div class="row">
            <div class="col-md-12">
                <div class="page-header">
                    <h2>Update Record</h2>
                </div>
                <p>Please edit the input values and submit to update the record.</p>
                <form action="<?php echo htmlspecialchars(basename($_SERVER['REQUEST_URI'])); ?>" method="post">
                    <div class="form-group <?php echo (!empty($firstname_err)) ? 'has-error' : ''; ?>">
                        <label>First Name</label>
                        <input type="text" name="firstname" class="form-control" value="<?php echo $firstname; ?>">
                        <span class="help-block"><?php echo $firstname_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($lastname_err)) ? 'has-error' : ''; ?>">
                        <label>Last Name</label>
                        <input type="text" name="lastname" class="form-control" value="<?php echo $lastname; ?>">
                        <span class="help-block"><?php echo $lastname_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($address_err)) ? 'has-error' : ''; ?>">
                        <label>Email</label>
                        <input type="email" name="email" class="form-control" value="<?php echo $email; ?>" />
                        <span class="help-block"><?php echo $email_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($address_err)) ? 'has-error' : ''; ?>">
                        <label>Address</label>
                        <textarea name="address" class="form-control"><?php echo $address; ?></textarea>
                        <span class="help-block"><?php echo $address_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($level_err)) ? 'has-error' : ''; ?>">
                        <label>Access Level</label>
                        <input type="text" name="level" class="form-control" value="<?php echo $level; ?>">
                        <span class="help-block"><?php echo $level_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($status_err)) ? 'has-error' : ''; ?>">
                        <label>Status</label>
                        <input type="text" name="status" class="form-control" value="<?php echo $status; ?>">
                        <span class="help-block"><?php echo $status_err;?></span>
                    </div>
                    <input type="hidden" name="id" value="<?php echo $id; ?>"/>
                    <input type="submit" class="btn btn-primary" value="Submit">
                    <a href="index.php" class="btn btn-default">Cancel</a>
                </form>
            </div>
        </div>
    </div>
</div>
</body>
</html>

Answer

<?php
// Include config file
require_once "config.php";

// Define variables and initialize with empty values
$firstname = $lastname = $email = $address = $status = $level = "";
$firstname_err = $lastname_err = $email_err = $address_err = $level_err = $status_err = "";

// Processing form data when form is submitted
if(isset($_POST["id"])){
    // Get hidden input value
    $id = $_POST["id"];

    // Validate name-first
    $input_firstname = trim($_POST["firstname"]);
    if(empty($input_firstname)){
        $firstname_err = "Please enter a first name.";
    } elseif(!filter_var($input_firstname, FILTER_VALIDATE_REGEXP, array("options"=>array("regexp"=>"/^[a-zA-Zs]+$/")))){
        $firstname_err = "Please enter a valid first name.";
    } else{
        $firstname = $input_firstname;
    }

    //Validate lastname
    $input_lastname = trim($_POST["lastname"]);
    if(empty($input_lastname)){
        $lastname_err = "Please enter a last name.";
    } elseif(!filter_var($input_lastname, FILTER_VALIDATE_REGEXP, array("options"=>array("regexp"=>"/^[a-zA-Zs]+$/")))){
        $lastname_err = "Please enter a valid last name.";
    } else{
        $lastname = $input_firstname;
    }

    //Validate email address
    $input_email = trim($_POST["email"]);
    if(empty($input_email)){
        $email_err = "Please enter an email address.";
    } else{
        $email = $input_email;
    }

    // Validate address 
    $input_address = trim($_POST["address"]);
    if(empty($input_address)){
        $address_err = "Please enter an address.";
    } else{
        $address = $input_address;
    }

    // Validate access level
    $input_level = trim($_POST["level"]);
    if(empty($input_level)){
        $level_err = "Please enter an level.";
    } elseif($input_level == 'Admin'){
        $level = $input_level;
    }elseif($input_level == 'Customer'){
        $level = $input_level;
    }else{
        $level_err = 'Please choose from Admin or Customer';
    }

    // Validate status
    $input_status = trim($_POST["status"]);
    if(empty($input_status)){
        $status_err = "Please enter a status";
    }elseif($input_status == '1'){
        $status = $input_status;
    }elseif($input_status == '0'){
        $status = $input_status;
    }else{
        $status_err = "Please enter a valid status";
    }
    
    echo "<script>alert('";
    echo "Checking all inputs vales---"; 
    echo $id; echo "=id--<br>";
    echo $input_firstname; echo "=fname---<br>";
    echo $input_lastname; echo "=lname---<br>";
    echo $input_email; echo "=email---<br>";
    echo $input_address; echo "=add---<br>";
    echo $input_level; echo "=level<br>";
    echo $input_status; echo "=stat<br>";
    echo "')</script> ";
    

    // Check input errors before inserting in database
    if(empty($firstname_err) && empty($lastname_err) && empty($email_err) && empty($address_err) && empty($level_err) && empty($status_err)){
        // Prepare an update statement
            echo "<script>alert('";
            echo "Im inside `Check Inputs before inserting in database` If Block... All Good so far"; echo "<br>"; 
            echo "')</script> ";
        $sql = "UPDATE users SET firstname=?, lastname=? address=?, email=?, access_level=?, status=? WHERE id=?";

        if($stmt = mysqli_prepare($link, $sql)){
            echo "<script>alert('";
            echo "Im inside `mysqli_prepare` If Block... All Good so far"; echo "<br>"; 
            echo "')</script> ";
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "sssssii", $param_firstname, $param_lastname, $param_address, $param_email, $param_level, $param_status, $param_id);

            // Set parameters
            $param_firstname = $firstname;
            $param_lastname = $lastname;
            $param_address = $address;
            $param_email = $email;            
            $param_level = $level;
            $param_status = $status;
            $param_id = $id;

            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Records updated successfully. Redirect to landing page
            echo "<script>alert('";
                echo "Im inside `mysqli_stmt_execute` If Block... All Good so far"; echo "<br>"; 
            echo "')</script> ";
                header("location: index.php");
                exit();
            } else{
            echo "<script>alert('";
                echo "Im inside `mysqli_stmt_execute` If Block... Not Good"; echo "<br>"; 
            echo "')</script> ";
                echo "Something went wrong. Please try again later.";
            }
            // Close statement
            mysqli_stmt_close($stmt);
        }else{
            echo "<script>alert('";
            echo "Im directly into else block from `empty input check If` Block... Not Good"; echo "<br>"; 
            echo "')</script> ";
            echo mysqli_stmt_error($stmt);
        }
    }

    // Close connection
    mysqli_close($link);
} else{
    // Check existence of id parameter before processing further
    if(isset($_GET["id"]) && !empty(trim($_GET["id"]))){
        // Get URL parameter
        $id =  trim($_GET["id"]);

        // Prepare a select statement
        $sql = "SELECT * FROM users WHERE id = ?";
        if($stmt = mysqli_prepare($link, $sql)){

            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "i", $param_id);

            // Set parameters
            $param_id = $id;

            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                $result = mysqli_stmt_get_result($stmt);

                if(mysqli_num_rows($result) == 1){
                    /* Fetch result row as an associative array. Since the result set contains only one row, we don't need to use while loop */
                    $row = mysqli_fetch_array($result, MYSQLI_ASSOC);

                    // Retrieve individual field value
                    $firstname = $row["firstname"];
                    $lastname = $row["lastname"];
                    $email = $row["email"];
                    $address = $row["address"];
                    $level = $row["access_level"];
                    $status = $row["status"];
                } else{
                    // URL doesn't contain valid id. Redirect to error page
                    header("location: error.php");
                    exit();
                }

            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }
        }

        // Close statement
        mysqli_stmt_close($stmt);

        // Close connection
        mysqli_close($link);
    }  else{
        // URL doesn't contain id parameter. Redirect to error page
        header("location: error.php");
        exit();
    }
}
?>

<?php
// core configuration
include_once "../../config/core.php";

// check if logged in as admin
include_once "../login_checker.php";

// set page title
$page_title = "Update Record";

// include page header HTML
include '../layout_head.php';

echo "<div class='col-md-12'>";

// get parameter values, and to prevent undefined index notice
$action = isset($_GET['action']) ? $_GET['action'] : "";

// tell the user he's already logged in
if ($action == 'already_logged_in') {
    echo "<div class='alert alert-info'>";
    echo "<strong>You</strong> are already logged in.";
    echo "</div>";
} else if ($action == 'logged_in_as_admin') {
    echo "<div class='alert alert-info'>";
    echo "<strong>You</strong> are logged in as admin.";
    echo "</div>";
}

echo "</div>";

//content when logged in
?>
<div class="wrapper" style="width: 500px; margin: 0 auto;">
    <div class="container-fluid">
        <div class="row">
            <div class="col-md-12">
                <div class="page-header">
                    <h2>Update Record</h2>
                </div>
                <p>Please edit the input values and submit to update the record.</p>
                <form action="<?php echo htmlspecialchars(basename($_SERVER['REQUEST_URI'])); ?>" method="post">
                    <div class="form-group <?php echo (!empty($firstname_err)) ? 'has-error' : ''; ?>">
                        <label>First Name</label>
                        <input type="text" name="firstname" class="form-control" value="<?php echo $firstname; ?>">
                        <span class="help-block"><?php echo $firstname_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($lastname_err)) ? 'has-error' : ''; ?>">
                        <label>Last Name</label>
                        <input type="text" name="lastname" class="form-control" value="<?php echo $lastname; ?>">
                        <span class="help-block"><?php echo $lastname_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($address_err)) ? 'has-error' : ''; ?>">
                        <label>Email</label>
                        <input type="email" name="email" class="form-control" value="<?php echo $email; ?>" />
                        <span class="help-block"><?php echo $email_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($address_err)) ? 'has-error' : ''; ?>">
                        <label>Address</label>
                        <textarea name="address" class="form-control"><?php echo $address; ?></textarea>
                        <span class="help-block"><?php echo $address_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($level_err)) ? 'has-error' : ''; ?>">
                        <label>Access Level</label>
                        <input type="text" name="level" class="form-control" value="<?php echo $level; ?>">
                        <span class="help-block"><?php echo $level_err;?></span>
                    </div>
                    <div class="form-group <?php echo (!empty($status_err)) ? 'has-error' : ''; ?>">
                        <label>Status</label>
                        <input type="text" name="status" class="form-control" value="<?php echo $status; ?>">
                        <span class="help-block"><?php echo $status_err;?></span>
                    </div>
                    <input type="hidden" name="id" value="<?php echo $id; ?>"/>
                    <input type="submit" class="btn btn-primary" value="Submit">
                    <a href="index.php" class="btn btn-default">Cancel</a>
                </form>
            </div>
        </div>
    </div>
</div>
</body>
</html>

I updated the code please run that code. I cannot guess more what else could be be wrong but i have added some echo to your code. please run it and find where is the error. Double check your bind_parameter type.they must be exactly same as your database table types. i only help you as giving u an example not the whole solution.

Now you can see the alert showing where are you so you can track down the problem

Hope it will help and solve your problem.