Split custom field value into nested array

Hello,

I am currently using WP Gridbuilder to filter my data stored in Meta Box Custom Fields (Woocommerce products).

One of the fields contains a string with many different type names, each separated by a comma.
Example:

Mercedes-Benz A220, BMW X6, VW Nutzfahrzeuge

I now need to filter all products by the individual vehicle models. For this I need the Meta Box Custom Field content as a nested array. Unfortunately, I don't seem to be doing this correctly. Where do I have the error and how should it read correctly?

add_filter(
	'wp_grid_builder/indexer/index_object',
	function( $rows, $object_id, $facet ) {

		if ( 9 !== $facet['id'] ) {
			return $rows;
		}

		$value = get_post_meta( $object_id, 'wccf_maschinenkompatibilitaet', true );

		if ( empty( $value ) ) {
			return $rows;
		}

		return [
			array_map(
				function( $value ) {
					return [
						'facet_value' => $value,
						'facet_name'  => $value,
					];
				},
				explode( ',', $value )
			),
		];
	},
	10,
	3
);

Thank you already