In Toast, there is potential for a redeemable to be greyed out and not able to be selected. In working with Toast and other clients, we found that the following tends to resolve this.
On the Toast Back End, check the "MMM Dollar Check Discount GUID" located in Marketing > Rewards.
This field is intended for the Open Check Discount GUID.
Not sure how to set this up? Toast's Punchh setup may be found here. https://central.toasttab.com/s/article/Punchh-2-0-Configuration
Double-check that the steps outlined in the above document have been completed and that discounts are applied to the entire brand and not a single store.