Custom Placeholder in Email Notification

Custom Placeholder in Email Notification

Hi,

We've added a custom fields in our Sales order like booking date and booking time, but when adding those as a place holder in sales order email notification template they don't change and we get the following message:
The following place holders were not replaced in this message:
${salesorder.cf_booking_date} ${salesorder.cf_booking_time}

Can you help in solving this problem urgently please?

Thanks
Mahmood