retrieving image in post from new field

Hi,

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Got the issue. You've added the prefix for the field ID, screenshot https://share.getcloudapp.com/DOuodQb7.

So the field ID when using the shortcode is flipimagesingle_image_ngobiqx24ya. Get more details in the tab Code of Field Groups.

add_filter( 'rwmb_meta_boxes', 'your_prefix_register_meta_boxes' );

function your_prefix_register_meta_boxes( $meta_boxes ) {
    $prefix = 'flipimage';

    $meta_boxes[] = [
        'title'      => esc_html__( 'Flip Image', 'text-domain' ),
        'id'         => 'flip-image',
        'post_types' => ['post', 'portfolio'],
        'context'    => 'side',
        'priority'   => 'low',
        'fields'     => [
            [
                'id'   => $prefix . 'single_image_ngobiqx24ya', //here
                'type' => 'single_image',
                'name' => esc_html__( 'Single Image', 'text-domain' ),
            ],
        ],
    ];

    return $meta_boxes;
}

Hi,

The PHP code is generated by the Builder, you can share it with other sites that do not have the MB Builder extension. And I've checked the code to see the settings of the meta box and custom fields. You can learn to use it in the documentation https://docs.metabox.io/extensions/meta-box-builder/#getting-php-code.