getting Invalid Email or Password in my localhost website

<?php

function accountLogin($userName, $userPassword){
    session_start();
    include('dbConnection.php');
    $password = md5($userPassword);

    $accountID = [];

    $query = "SELECT * FROM tbl_account WHERE `accountID` = '" . $userName . "' AND `accountActive` = '1'"; //QUERY CODE
    $sql = mysqli_query($conn, $query) or die("System Error: " . mysqli_error($conn)); //SENDING QUERY TO DATABASE

    //DOES QUERY CONTAINS ROWS?
    if(mysqli_num_rows($sql)>0){
        $row = mysqli_fetch_assoc($sql);
        extract($row);

        if($accountPassword==$password){
            $_SESSION['userID'] = $accountID;
            $_SESSION['fName'] = $accountFName;
            
            return 1;
        }
        else{
            return 0;
        }
    }
    else{
        return 0;
    }
    
}

?>

What seems to be the problem?