rwmb_set_meta for custom table

Hi,

I am hooking into a function of the wp all import-plugin to readout data from a serialized regular custom field and move it over to a metabox-field, which is in a custom table. this is my code to loop through the various fields:

 
    $data = get_post_meta( $postid, 'all_data', true);

$fields = [
        'address',
        'city',
        'zip',
        'state',
        'email',
        'url',
        'phone'
    ];

    // Loop through data
    foreach( $fields as $field ) {
        if( array_key_exists( $field, $data ) ) {
            rwmb_set_meta(
                $postid,
                $field,
                sanitize_text_field( $data[$field] )
            );
        }
    }

If I push data to error_log I can see all the necessary data. However, rwmb_set_meta does not save anything. My custom table is empty 🙁

What do I do wrong?