[NSFW] Custom checkbox checked should be true but is false

Hi,

We have added a custom checkbox to Klarna checkout:

function add_omnisend_kco_checkbox( $additional_checkboxes ) {
	$additional_checkboxes[] = array(
		'id'       => 'omnisend_kco_checkbox',
		'text'     => 'Hold meg oppdatert p? nyheter og tilbud.',
		'checked'  => false,
		'required' => false,
	);
	return $additional_checkboxes;
}
add_filter( 'kco_additional_checkboxes', 'add_omnisend_kco_checkbox' );

Using this callback function:

function kco_process_checkboxes( $order_id ) {
    $klarna_order_id = get_post_meta( $order_id, '_transaction_id', true );
	$klarna_order    = KCO_WC()->api->get_klarna_order( $klarna_order_id );

	if ( isset( $klarna_order['merchant_requested']['additional_checkboxes'] ) ) {
		foreach ( $klarna_order['merchant_requested']['additional_checkboxes'] as $checkbox ) {
			error_log(json_encode($checkbox));
		}
	}
}
add_action( 'kco_wc_payment_complete', 'kco_process_checkboxes' );

The problem is that checked is always false:

[15-Aug-2024 12:36:39 UTC] {"id":"omnisend_kco_checkbox","checked":false}

The only way we made it work was by changing ‘checked’ => true, in add_omnisend_kco_checkbox. How can we fix this?