Meta Box

But then the validate message doesn't show?

I just wanna redirect to the form like this (it stays on the same site, but scrolls to the form) https://www.sikkerfangst.dk/produkt/en-ordentlig-fiskestang#auktionsbud

Your example works, but then the message doesn't show.

Nope it still doesn't save anything but the last. I tried everything in the docs.

<?php
add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );

function your_prefix_function_name( $meta_boxes ) {
    $prefix = '';

    $meta_boxes[] = [
        'title'      => __( 'Produkt info', 'your-text-domain' ),
        'id'         => 'produkt-info',
        'post_types' => ['produkt'],
        'fields'     => [
            [
                'name'           => __( 'Produkttype', 'your-text-domain' ),
                'id'             => $prefix . 'produkttype',
                'type'           => 'taxonomy',
                'taxonomy'       => ['category'],
                'field_type'     => 'select_advanced',
                'remove_default' => true,
                'required'       => true,
                'query_args'     => [
                    'child_of' => 4,
                ],
            ],
            [
                'name'    => __( 'Dage på auktion', 'your-text-domain' ),
                'id'      => $prefix . 'dage_paa_auktion',
                'type'    => 'number',
                'max'     => 21,
                'append'  => 'Dage',
                'visible' => [
                    'when'     => [['produkttype', '=', 7]],
                    'relation' => 'or',
                ],
            ],
            [
                'name'    => __( 'Startpris', 'your-text-domain' ),
                'id'      => $prefix . 'startpris',
                'type'    => 'number',
                'min'     => 0,
                'max'     => 100000,
                'append'  => 'DKK',
                'visible' => [
                    'when'     => [['produkttype', '=', 7]],
                    'relation' => 'or',
                ],
            ],
            [
                'name'    => __( 'Bud step', 'your-text-domain' ),
                'id'      => $prefix . 'bud_step',
                'type'    => 'number',
                'max'     => 500,
                'visible' => [
                    'when'     => [['produkttype', '=', 7]],
                    'relation' => 'or',
                ],
            ],
            [
                'name'    => __( 'Max Pris', 'your-text-domain' ),
                'id'      => $prefix . 'max_pris',
                'type'    => 'number',
                'min'     => 0,
                'max'     => 100000,
                'append'  => 'DKK',
                'visible' => [
                    'when'     => [['produkttype', '=', 5]],
                    'relation' => 'or',
                ],
            ],
            [
                'name'    => __( 'Pris', 'your-text-domain' ),
                'id'      => $prefix . 'pris',
                'type'    => 'number',
                'min'     => 0,
                'max'     => 100000,
                'visible' => [
                    'when'     => [['produkttype', '=', 6]],
                    'relation' => 'or',
                ],
            ],
            [
                'name'     => __( 'Beskrivelse', 'your-text-domain' ),
                'id'       => $prefix . 'beskrivelse',
                'type'     => 'textarea',
                'required' => true,
            ],
            [
                'name'             => __( 'Billeder', 'your-text-domain' ),
                'id'               => $prefix . 'billeder',
                'type'             => 'image_upload',
                'max_file_uploads' => 4,
            ],
            [
                'name'           => __( 'Betalingsmidler', 'your-text-domain' ),
                'id'             => $prefix . 'betalingsmiddel',
                'type'           => 'taxonomy',
                'taxonomy'       => ['category'],
                'field_type'     => 'select_advanced',
                'remove_default' => true,
                'multiple'       => true,
                'required'       => true,
                'query_args'     => [
                    'child_of' => 36,
                ],
            ],
            [
                'name'           => __( 'Forsendelsesmuligheder', 'your-text-domain' ),
                'id'             => $prefix . 'forsendelsesmulighed',
                'type'           => 'taxonomy',
                'taxonomy'       => ['category'],
                'field_type'     => 'select_advanced',
                'remove_default' => true,
                'multiple'       => true,
                'required'       => true,
                'query_args'     => [
                    'child_of' => 28,
                ],
            ],
            [
                'name'       => __( 'Auktionen er slut', 'your-text-domain' ),
                'id'         => $prefix . 'auktionen_er_slut',
                'type'       => 'switch',
                'style'      => 'rounded',
                'on_label'   => 'Ja',
                'off_label'  => 'Nej',
                'attributes' => [
                    'readonly' => true,
                ],
                'visible'    => [
                    'when'     => [['produkttype', '=', 7]],
                    'relation' => 'or',
                ],
            ],
        ],
    ];

    return $meta_boxes;
}