return to serial purchased and send sms

Hi,

1. That's right you'll need to develop a plugin for that. You'll want to implement the onAfterOrderUpdate trigger:
www.hikashop.com/support/documentation/6...#onBeforeOrderUpdate
Using that trigger, you'll have the order_id in $order->order_id. Then, you can load the serials of thar order with a MySQL query on the table hikaserial_serial with a WHERE on the column serial_order_id being equal to that $order->order_id variable.

2. No, that information is not supported by payment plugins so it would require modifying the code of the payment plugin to do that. With just the settings available, that's not possible.