How do we display a \Popup message\""

Hi,

You can use Show popup step in a Data Flow and map the output of DataFlow with the File upload control.
Following are the steps to do it :
1. Create a Flow.
2. Add a File upload control and a button in the form.
3. Click on Form surface and create a Data Flow.
4. Insert a Show popup step -> Configure Inputs Subject and Message.
5. Save the Data Flow and Update Inputs.
6. Run the Flow and upload the file.