Hi! Since there are no standard WooCommerce emails that are sent out for this status, you cannot do this out of the box.
You can manually send the WooCommerce customer invoice email (make sure you have checked that email in the General settings tab of the PDF invoice plugin), or make this email being sent out automatically on these statuses. Add this to your theme functions:
add_action( 'woocommerce_order_status_pending_to_on-hold_notification', array(WC()->mailer()->emails['WC_Email_Customer_Invoice'],'trigger' ) );
This will send out the Invoice email when the order status changes from pending payment (which is always a temporary status and expires) to on-hold.
If you haven’t edited your theme functions before, make sure to read this first.
Just saw that the next version of WooCommerce will finally get a separate On-Hold email, yay!
Hope that helps ??
Ewout
