The Selection that triggered the application of this discount
| quantity | number <double>  The amount of the selection used to trigger the applied discount.  | 
object (ExternalReference)  A wrapper object with fields that allow reference to a Toast entity by Toast GUID.  | 
{- "selection": {
- "guid": "string",
 - "entityType": "string",
 - "externalId": "string"
 
}, - "quantity": 0
 
}