I have a workflow with two 'Respond to a PowerApp' actions at the end, which output will cause a text label to pop up in my PowerApp to confirm whether the flow has succeeded.

For this purpose, I have created a variable in the app called 'varNewScheduleCreated' whose value equals the NewScheduleCreated output resulting from the flow (either 'true' or 'false').
My alert text label has its Visible property set to 'varNewScheduleCreated' so it should appear once the flow is completed with a 'true' outcome.
Finally, I have a button whose 'OnSelect' property is set to 'Set(varNewScheduleCreated,false)', so by clicking I can hide the alert text label once I'm done.
The process built as described above doesn't work and I receive the following message when trying to use 'varNewScheduleCreated' for the 'OnSelect' property of the button.

Thanks for helping!