Do you see the values of the mmulti dropdown in the preview?
What parameters is the backend workflow taking as input?
How are you scheduling the backend workflow? How are you passing the inputs?
How do you tell that the workflow is not reading the parameters?
Have you checked the logs to see what parameters are passed to the backend workflow? (remember to select “schedued task to run”, “request for api workflow” and “scheduled task comleted” from the “show advanced” panel of the logs)