Dear {Recipient},
Please be informed that your shipment with order number {order number} will be arriving {number of}
{days/weeks} later than originally estimated. The delay is due to {an unusually large demand for the product recently/an error in our system/other reason}. We apologize for the inconvenience.
We would like to offer you a voucher which you can use to avail of a {number}% discount on your next
purchase. Please do not hesitate to contact customer service should you have any questions regarding your order.
Thank you for your kind understanding.
Warmest regards,
{Your Name},
{Your Position}