You just pass the JSON as a string, then convert it in the desktop flow.
Copy this code into your PAD designer to see how it works.
SET Input_JSON TO $'''{
\"name\":\"John\",
\"age\":30,
\"cars\":[\"Ford\", \"BMW\", \"Fiat\"]
}'''
Variables.ConvertJsonToCustomObject Json: Input_JSON CustomObject=> JsonAsCustomObject
LOOP FOREACH Current_Car IN JsonAsCustomObject['cars']
Display.ShowMessageDialog.ShowMessageWithTimeout Message: Current_Car Icon: Display.Icon.None Buttons: Display.Buttons.OK DefaultButton: Display.DefaultButton.Button1 IsTopMost: True Timeout: 3
END