Olo can send down a discount to Toast POS if a discount is configured correctly in Toast. Once the Discount is created in Toast, it can be linked in Olo using the GUID generated by Toast. At this time (2/22/2018), Olo can only send an Open Dollar, Order Level Discount to Toast, so it will need to be configured as such in Toast. Below is a screenshot of how the discount needs to be configured in Toast.
Once the discount has been created in Toast, you can create desired discount in the Olo Dashboard. The Toast GUID is showed in the URL for the specific Discount Details page as seen below. Once the discount is created in the Olo Dashboard, you can copy the GUID from the URL, and use it in the POS Reference field with a "C*" in front of the value. For example C*00000000-0000-0000-0000-000000000000