Do not insert the fields in Mysql from PHP

How about. in my case I use PDO.

to make the insertion. This is an example.

<?php
    include_once "conexion.php";
    if(isset($_POST)){
        if(isset($_POST['name']) && 
           isset($_POST['last_name']) && 
           isset($_POST['email']) && 
           isset($_POST['password'])){
                $nombre = $_POST['name'];
                $last_name = $_POST['last_name'];
                $email = $_POST['email'];
                $password = $_POST['password'];

                //Ejecutar una sentencia preparada vinculando varialbes de PHP 

                $gsent = $pdo->prepare('INSERT INTO users (name, last_name, email, password)
                                        VALUES (:name,:last_name,:email,:password)');
                $gsent->bindParam(':name', $nombre, PDO::PARAM_STR);
                $gsent->bindParam(':last_name', $last_name, PDO::PARAM_STR);
                $gsent->bindParam(':email', $email, PDO::PARAM_STR);
                $gsent->bindParam(':password', $password, PDO::PARAM_STR);
                $state= $gsent->execute();
                if($state){
                    echo 'Datos ingresados';
                }
                else{
                    echo 'Datos NO Ingresados';
                }
                $pdo= null;
        }   
    } 
?>

Where you include your connection.

where $state returns as boolea. If it still does not solve your doubt. I invite you to revices the documentation of PHP mysql Greetings