Background image doesn't render in Gutenberg

Hi Peter,

this code also works for me in the frontend, but not in the backend (Gutenberg). The image isn't visible in the editor.

I think, not the registration is the problem, cause the output of the variable ($image_url) is ok.

I register the block with this code:

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

function custom_blocks_mc_teaser_boxes( $meta_boxes ) {
    $prefix = 'mc-';

    $meta_boxes[] = [
        'title'           => __( 'MC Teaser Boxen', 'custom-blocks' ),
        'id'              => 'mc-teaser-boxes',
        'description'     => 'MC Teaser Boxen',
        'icon' => [
            'background' => '#c2b7ae',
            'foreground' => '#fff',
            'src' => 'images-alt',
        ],
        'category'        => 'mc',
        'keywords'        => ['teaser', 'box', 'mc'],
        'supports'        => [
            'align' => ['left', 'right', 'center', 'wide', 'full'],
        ],
        'render_template' => plugin_dir_path( __FILE__ ) . 'template.php',
        'enqueue_assets' => function() {
            wp_enqueue_style( 'mc-teaser-boxes-styles', plugin_dir_url( __FILE__ ) . 'mc-teaser-boxes-styles.css' );
        },
        'type'            => 'block',
        'context'         => 'side',
        'fields'          => [
            [
                'type' => 'group',
                'id'   => 'teaser-boxes-rows',
                'name' => 'MC-Teaser-Elemente',
                'group_title' => 'Teaser {#}',
                'clone' => true,
                'sort_clone' => true,
                'collapsible' => true,
                'fields' => [
                
                    [
                        'name'              => __( 'Bild', 'custom-blocks' ),
                        'id'                => $prefix . 'teaser-boxes-img',
                        'type'              => 'single_image',
                        'required'          => true,
                    ],
                    [
                        'name'              => __( 'Überschrift (fett)', 'custom-blocks' ),
                        'id'                => $prefix . 'teaser-boxes-headline',
                        'type'              => 'text',
                    ],
                ],
            ],
        ],
    ];

    return $meta_boxes;
}

and this is the template:

<div class="mc-teaser-boxes">
    <div class="mc-teaser-boxes-wrap">
        <?php
        $groups = mb_get_block_field( 'teaser-boxes-rows' );
        foreach ( $groups as $group ) {
            $image = RWMB_Image_Field::file_info( $group['mc-teaser-boxes-img'], ['size' => 'full'] );
            
            echo '<div class="teaser-boxes-sub">';
                echo '<div class="mc-teaser-boxes-bg-box">';
                    echo '<div class="mc-teaser-boxes-img" style="background-image: url('.$image['url'].')"></div>';
                    echo '<div class="mc-teaser-boxes-border">';
                        echo '<div class="mc-teaser-boxes-txt-box">';
                            echo '<h3>'.$group['mc-teaser-boxes-headline'].'</h3>';
                            echo '<p>'.$image['url'].'</p>';
                        echo '</div>';
                    echo '</div>';
                echo '</div>';
        }
        ?>
    </div>
</div>

I put $image['url'] in a paragraph tag for debugging. You will see, the url is ok.

Thanks!