remote validation in group Fields possible

Hello,

Can you share the code that creates the group field? You should add the subfield ID to the remote validation. Here is an example:

add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );

function your_prefix_function_name( $meta_boxes ) {
    $meta_boxes[] = [
        'title'    => __( 'My Post Meta1', 'your-text-domain' ),
        'id'       => 'my-post-meta1',
        'fields'     => [            
            [
                'name'            => __( 'Group', 'your-text-domain' ),
                'id'              => 'group',
                'type'            => 'group',
                'fields'          => [
                    [
                        'name'            => __( 'Text', 'your-text-domain' ),
                        'id'              => 'text',
                        'type'            => 'text',           
                    ],
                ],
            ],
        ],
        'validation' => [
            'rules'    => [
                'text' => [
                    'remote' => admin_url( 'admin-ajax.php?action=my_action1' )
                ]
            ],
            'messages' => [
                'text' => [
                    'remote' => __( 'test remote validation', 'your-text-domain' )
                ]
            ],
        ],
    ];

    return $meta_boxes;
}

add_action( 'wp_ajax_my_action1', function () {
    if ( $_GET['text'] === 'something' ) {
        echo 'true'; // Valid
    } else {
        echo 'false'; // Invalid
    }
    die;
} );