Convergeter string array and save to database with Codeignater

Question

I have a checkbox set to send as a string to the database for the same comma-separated field, however I am getting a return to convert to string array as below:

In the controller I have the following method to handle the checkbox:

if( isset( $_POST['documento'] ) && is_array( $_POST['documento'] ) ) {
    $documentos = implode( ', ', $_POST['documento'] );
} else {
    $documentos = '';
}

In the view, the checkbox:

<div class="customcheck">
      <input type="checkbox" value="RG" name="documento[]">
      <input type="checkbox" value="CPF" name="documento[]">
      
</div>

Answer 1

I tested it like this and it worked:

<form action="resposta.php" method="POST">
    <input type="checkbox" value="RG" name="documento[]">
    <input type="checkbox" value="CPF" name="documento[]">
    <input type="checkbox" value="certidão" name="documento[]">
    <input type="checkbox" value="titulo" name="documento[]">
    <input type="checkbox" value="CPF" name="documento[]">
    <input type="submit" value="Enviar">
</form>

php response file.:

if (isset($_POST['documento']) && is_array($_POST['documento'])) {
    $documentos = implode(', ', $_POST['documento']);
} else {
    $documentos = '';
}

$username = '****';
$password = '****';

try {
    $pdo = new PDO('mysql:host=localhost;dbname=stackoverflow', $username, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $sql = "INSERT INTO documentos (documentos) VALUES (?)";
    $stmt = $pdo->prepare($sql);
    $stmt->execute([$documentos]);

    echo "Enviado com sucesso!";

} catch (PDOException $e) {

    echo 'ERROR: ' . $e->getMessage();
}

database:

CREATE TABLE `documentos` (
  `id` int(11) NOT NULL,
  `documentos` varchar(255) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

ALTER TABLE `documentos`
  ADD PRIMARY KEY (`id`);