Mysql Bind, Number of elements do not match the bind value

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I can’t fathom where i went wrong on this instruction. I keep getting the warning that number of elements does not match the bind value. I’m trying to validate a field for country where users can select the country they are registering from but whenever i run a test on xampp i get the warning whilst the information aren’t sent to the database.

I’m not sure if my code is liable to sql injections since I’m new to php and mysql. If i remove the country function the form works properly. I don’t not think the error is from the html form so I’d rather not uploaded it here.

Here’s the php code.

<?php
// Include config file
require_once "db.php";
 
// Define variables and initialize with empty values
$username = $password = $confirm_password = $country = "";
$username_err = $password_err = $confirm_password_err = $country_err = "";
 
// Processing form data when form is submitted
if($_SERVER["REQUEST_METHOD"] == "POST"){
 
    // Validate username
    if(empty(trim($_POST["username"]))){
        $username_err = "Please enter a username.";
    } else{
        // Prepare a select statement
        $sql = "SELECT id FROM users WHERE username = ?";
        
        if($stmt = mysqli_prepare($db, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "s", $param_username);
            
            // Set parameters
            $param_username = trim($_POST["username"]);
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                /* store result */
                mysqli_stmt_store_result($stmt);
                
                if(mysqli_stmt_num_rows($stmt) == 1){
                    $username_err = "This username is already taken.";
                } else{
                    $username = trim($_POST["username"]);
                }
            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }

            // Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Validate password
    if(empty(trim($_POST["password"]))){
        $password_err = "Please enter a password.";     
    } elseif(strlen(trim($_POST["password"])) < 6){
        $password_err = "Password must have atleast 6 characters.";
    } else{
        $password = trim($_POST["password"]);
    }
    
    // Validate confirm password
    if(empty(trim($_POST["confirm_password"]))){
        $confirm_password_err = "Please confirm password.";     
    } else{
        $confirm_password = trim($_POST["confirm_password"]);
        if(empty($password_err) && ($password != $confirm_password)){
            $confirm_password_err = "Password did not match.";
        }
    }
    

      // Validate Country
    if(empty(trim($_POST["country"]))){
        $country_err = "Please Choose a Country.";     
    } 
         else{
        $country = trim($_POST["country"]);
    }



    // Check input errors before inserting in database
    if(empty($username_err) && empty($password_err) && empty($confirm_password_err)){
        
        // Prepare an insert statement
        $sql = "INSERT INTO users (username, password, country) VALUES (?, ?, ?)";
         
        if($stmt = mysqli_prepare($db, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "ss", $param_username, $param_password, $param_country);
            
            // Set parameters
            $param_country = $country;
            $param_username = $username;
            $param_password = password_hash($password, PASSWORD_DEFAULT); // Creates a password hash
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Redirect to login page
                header("location: login.php");
            } else{
                echo "Something went wrong. Please try again later.";
            }

            // Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Close connection
    mysqli_close($db);
}
?>.
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