If you'd like to set up promote code for online ordering, please refer to the following steps and modify in backhouse :
Login Backhouse > Online Ordering > Promotion settings
Click Add Promotion > Select Promo code
Key in the Promotion name, Promo Code and settings like Discount percentage.
Hit Save to finish the settings
If your promote code is open for public to use,
you can set up the announcement on online ordering page.
For announcement settings steps, kindly refer to this article.