Hi Cedric,
To be able to set a custom attribute for title, you need to create a text field and put it in the meta box (which has ID in the shortcode), like this:
add_filter( 'rwmb_meta_boxes', function( $meta_boxes ) {
$meta_boxes[] = [
'title' => 'Your title',
'id' => 'your-id',
'fields' => [
[
'title' => 'Post title',
'id' => 'post_title',
'disabled' => true,
],
// Other fields here
],
];
} );
And in your shortcode, don't include the post_fields parameter:
[mb_frontend_form id="your-id"]
